diff --git a/lib/db/migrations/001_initial.sql b/lib/db/migrations/001_initial.sql
new file mode 100644
index 0000000..a680f91
--- /dev/null
+++ b/lib/db/migrations/001_initial.sql
@@ -0,0 +1,257 @@
+-- 001_initial.sql
+-- シンプルグループウェア 初期スキーマ
+-- 全16テーブル + インデックス
+
+-- 1. users: システム利用ユーザー
+CREATE TABLE users (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  name TEXT NOT NULL,
+  email TEXT NOT NULL UNIQUE,
+  password_hash TEXT,
+  avatar_url TEXT,
+  role TEXT NOT NULL DEFAULT 'member',
+  status TEXT NOT NULL DEFAULT 'active',
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL
+);
+
+-- 2. projects: プロジェクト
+CREATE TABLE projects (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  name TEXT NOT NULL,
+  description TEXT,
+  status TEXT NOT NULL DEFAULT 'active',
+  owner_id INTEGER NOT NULL,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  FOREIGN KEY (owner_id) REFERENCES users(id)
+);
+
+-- 3. project_members: プロジェクトメンバー
+CREATE TABLE project_members (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  user_id INTEGER NOT NULL,
+  role TEXT NOT NULL DEFAULT 'member',
+  joined_at TEXT NOT NULL,
+  UNIQUE(project_id, user_id),
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+  FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+);
+
+-- 4. board_threads: 掲示板スレッド
+CREATE TABLE board_threads (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  title TEXT NOT NULL,
+  body_md TEXT NOT NULL,
+  author_id INTEGER NOT NULL,
+  category TEXT,
+  is_pinned INTEGER NOT NULL DEFAULT 0,
+  is_important INTEGER NOT NULL DEFAULT 0,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  deleted_at TEXT,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+  FOREIGN KEY (author_id) REFERENCES users(id)
+);
+
+-- 5. board_comments: 掲示板コメント
+CREATE TABLE board_comments (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  thread_id INTEGER NOT NULL,
+  author_id INTEGER NOT NULL,
+  body_md TEXT NOT NULL,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  deleted_at TEXT,
+  FOREIGN KEY (thread_id) REFERENCES board_threads(id) ON DELETE CASCADE,
+  FOREIGN KEY (author_id) REFERENCES users(id)
+);
+
+-- 6. chat_messages: チャットメッセージ
+CREATE TABLE chat_messages (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  author_id INTEGER NOT NULL,
+  body TEXT NOT NULL,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  deleted_at TEXT,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+  FOREIGN KEY (author_id) REFERENCES users(id)
+);
+
+-- 7. todo_columns: ToDoカラム
+CREATE TABLE todo_columns (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  name TEXT NOT NULL,
+  order_index INTEGER NOT NULL DEFAULT 0,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE
+);
+
+-- 8. todo_items: ToDoタスク
+CREATE TABLE todo_items (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  column_id INTEGER NOT NULL,
+  title TEXT NOT NULL,
+  description TEXT,
+  assignee_id INTEGER,
+  creator_id INTEGER NOT NULL,
+  priority TEXT NOT NULL DEFAULT 'normal',
+  start_date TEXT,
+  due_date TEXT,
+  completed_at TEXT,
+  order_index INTEGER NOT NULL DEFAULT 0,
+  milestone_id INTEGER,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  deleted_at TEXT,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+  FOREIGN KEY (column_id) REFERENCES todo_columns(id) ON DELETE CASCADE,
+  FOREIGN KEY (assignee_id) REFERENCES users(id),
+  FOREIGN KEY (creator_id) REFERENCES users(id)
+);
+
+-- 9. file_assets: ファイルアセット
+CREATE TABLE file_assets (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  uploader_id INTEGER NOT NULL,
+  filename TEXT NOT NULL,
+  original_name TEXT NOT NULL,
+  mime_type TEXT NOT NULL,
+  size INTEGER NOT NULL,
+  path TEXT NOT NULL,
+  created_at TEXT NOT NULL,
+  deleted_at TEXT,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+  FOREIGN KEY (uploader_id) REFERENCES users(id)
+);
+
+-- 10. project_notes: Markdownメモ
+CREATE TABLE project_notes (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  title TEXT NOT NULL,
+  body_md TEXT NOT NULL,
+  tags TEXT,
+  is_pinned INTEGER NOT NULL DEFAULT 0,
+  created_by_id INTEGER NOT NULL,
+  updated_by_id INTEGER NOT NULL,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  deleted_at TEXT,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+  FOREIGN KEY (created_by_id) REFERENCES users(id),
+  FOREIGN KEY (updated_by_id) REFERENCES users(id)
+);
+
+CREATE INDEX idx_project_notes_project_id ON project_notes(project_id);
+CREATE INDEX idx_project_notes_updated_at ON project_notes(updated_at);
+
+-- 11. milestones: マイルストーン
+CREATE TABLE milestones (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  title TEXT NOT NULL,
+  description TEXT,
+  due_date TEXT,
+  status TEXT NOT NULL DEFAULT 'open',
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  deleted_at TEXT,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE
+);
+
+-- 12. calendar_events: カレンダーイベント
+CREATE TABLE calendar_events (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  title TEXT NOT NULL,
+  description TEXT,
+  type TEXT NOT NULL,
+  start_at TEXT NOT NULL,
+  end_at TEXT,
+  created_by_id INTEGER NOT NULL,
+  related_todo_id INTEGER,
+  related_milestone_id INTEGER,
+  related_meeting_id INTEGER,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  deleted_at TEXT,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+  FOREIGN KEY (created_by_id) REFERENCES users(id)
+);
+
+-- 13. meetings: ミーティング
+CREATE TABLE meetings (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  title TEXT NOT NULL,
+  description TEXT,
+  location TEXT,
+  meeting_url TEXT,
+  start_at TEXT NOT NULL,
+  end_at TEXT NOT NULL,
+  agenda_md TEXT,
+  minutes_md TEXT,
+  created_by_id INTEGER NOT NULL,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  deleted_at TEXT,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+  FOREIGN KEY (created_by_id) REFERENCES users(id)
+);
+
+-- 14. meeting_members: ミーティング参加メンバー
+CREATE TABLE meeting_members (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  meeting_id INTEGER NOT NULL,
+  user_id INTEGER NOT NULL,
+  status TEXT NOT NULL DEFAULT 'invited',
+  UNIQUE(meeting_id, user_id),
+  FOREIGN KEY (meeting_id) REFERENCES meetings(id) ON DELETE CASCADE,
+  FOREIGN KEY (user_id) REFERENCES users(id)
+);
+
+-- 15. notifications: 通知
+CREATE TABLE notifications (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  user_id INTEGER NOT NULL,
+  project_id INTEGER,
+  type TEXT NOT NULL,
+  title TEXT NOT NULL,
+  body TEXT,
+  read_at TEXT,
+  created_at TEXT NOT NULL,
+  FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE
+);
+
+-- 16. activity_logs: アクティビティログ
+CREATE TABLE activity_logs (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  project_id INTEGER NOT NULL,
+  actor_id INTEGER NOT NULL,
+  action TEXT NOT NULL,
+  target_type TEXT NOT NULL,
+  target_id INTEGER,
+  metadata_json TEXT,
+  created_at TEXT NOT NULL,
+  FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+  FOREIGN KEY (actor_id) REFERENCES users(id)
+);
+
+CREATE INDEX idx_activity_logs_project_id ON activity_logs(project_id);
+CREATE INDEX idx_activity_logs_created_at ON activity_logs(created_at);
+CREATE INDEX idx_notifications_user_id ON notifications(user_id);
+CREATE INDEX idx_chat_messages_project_id ON chat_messages(project_id);
+CREATE INDEX idx_board_threads_project_id ON board_threads(project_id);
+CREATE INDEX idx_todo_items_project_id ON todo_items(project_id);
+CREATE INDEX idx_meetings_project_id ON meetings(project_id);
+CREATE INDEX idx_calendar_events_project_id ON calendar_events(project_id);
diff --git a/lib/db/migrator.ts b/lib/db/migrator.ts
new file mode 100644
index 0000000..20398c9
--- /dev/null
+++ b/lib/db/migrator.ts
@@ -0,0 +1,68 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import { SqliteDatabase } from './sqlite';
+
+/**
+ * SQLファイルベースのMigration機構。
+ * - Migrationファイルをファイル名順に実行する
+ * - 実行済みファイルは再実行しない
+ * - 1ファイルごとにトランザクションを張り、失敗時はロールバックする
+ */
+export class Migrator {
+  constructor(
+    private readonly db: SqliteDatabase,
+    private readonly migrationsDir: string
+  ) {}
+
+  /**
+   * 未適用のMigrationをファイル名順に実行する
+   */
+  migrate(): void {
+    this.ensureMigrationsTable();
+
+    const applied = this.db.query<{ filename: string }>(
+      'SELECT filename FROM schema_migrations'
+    );
+    const appliedSet = new Set(applied.map((x) => x.filename));
+
+    const files = fs
+      .readdirSync(this.migrationsDir)
+      .filter((file) => file.endsWith('.sql'))
+      .sort();
+
+    for (const file of files) {
+      if (appliedSet.has(file)) continue;
+
+      const fullPath = path.join(this.migrationsDir, file);
+      const sql = fs.readFileSync(fullPath, 'utf-8');
+
+      this.db.transaction(() => {
+        this.db.exec(sql);
+        this.db.execute(
+          `INSERT INTO schema_migrations (filename, applied_at) VALUES (@filename, @appliedAt)`,
+          { filename: file, appliedAt: new Date().toISOString() }
+        );
+      });
+    }
+  }
+
+  /**
+   * 適用済みMigration一覧を取得する
+   */
+  getAppliedMigrations(): { filename: string; applied_at: string }[] {
+    this.ensureMigrationsTable();
+    return this.db.query<{ filename: string; applied_at: string }>(
+      'SELECT filename, applied_at FROM schema_migrations ORDER BY filename'
+    );
+  }
+
+  private ensureMigrationsTable(): void {
+    this.db.execute(`
+      CREATE TABLE IF NOT EXISTS schema_migrations (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        filename TEXT NOT NULL UNIQUE,
+        applied_at TEXT NOT NULL
+      )
+    `);
+  }
+}
diff --git a/lib/db/run-migrations.ts b/lib/db/run-migrations.ts
new file mode 100644
index 0000000..0475038
--- /dev/null
+++ b/lib/db/run-migrations.ts
@@ -0,0 +1,26 @@
+import path from 'node:path';
+import fs from 'node:fs';
+import { getDb, resetDbInstance } from './sqlite';
+import { Migrator } from './migrator';
+
+const migrationsDir = path.join(process.cwd(), 'lib', 'db', 'migrations');
+const dbPath = process.env.SQLITE_PATH ?? './data/app.db';
+
+const dbDir = path.dirname(dbPath);
+if (!fs.existsSync(dbDir)) {
+  fs.mkdirSync(dbDir, { recursive: true });
+}
+
+const db = getDb();
+const migrator = new Migrator(db, migrationsDir);
+
+migrator.migrate();
+
+const applied = migrator.getAppliedMigrations();
+console.log(`Migrations applied: ${applied.length}`);
+for (const m of applied) {
+  console.log(`  - ${m.filename} (applied at ${m.applied_at})`);
+}
+
+db.close();
+resetDbInstance();
diff --git a/lib/db/sqlite.ts b/lib/db/sqlite.ts
new file mode 100644
index 0000000..bf6a466
--- /dev/null
+++ b/lib/db/sqlite.ts
@@ -0,0 +1,98 @@
+import Database from 'better-sqlite3';
+
+export type SqlParams = Record<string, unknown> | unknown[];
+
+export interface ExecuteResult {
+  changes: number;
+  lastInsertRowid: number | bigint;
+}
+
+/**
+ * SQLiteへのアクセスを一元管理する共通SQLラッパー。
+ * 各Repositoryは直接better-sqlite3を触らず、必ずこのクラスを通してSQLを実行する。
+ */
+export class SqliteDatabase {
+  private db: Database.Database;
+
+  constructor(dbPath: string) {
+    this.db = new Database(dbPath);
+
+    this.db.pragma('journal_mode = WAL');
+    this.db.pragma('foreign_keys = ON');
+  }
+
+  /**
+   * 複数行を取得するSELECT
+   */
+  query<T>(sql: string, params?: SqlParams): T[] {
+    return this.db.prepare(sql).all(params ?? {}) as T[];
+  }
+
+  /**
+   * 単一行を取得するSELECT（該当なしの場合はnull）
+   */
+  get<T>(sql: string, params?: SqlParams): T | null {
+    const row = this.db.prepare(sql).get(params ?? {}) as T | undefined;
+    return row ?? null;
+  }
+
+  /**
+   * INSERT / UPDATE / DELETEを実行する（単一プリペアドステートメント）
+   */
+  execute(sql: string, params?: SqlParams): ExecuteResult {
+    const result = this.db.prepare(sql).run(params ?? {});
+
+    return {
+      changes: result.changes,
+      lastInsertRowid: result.lastInsertRowid,
+    };
+  }
+
+  /**
+   * 複数ステートメントを含むSQLを一括実行する（Migration用・パラメータバインド不可）。
+   * better-sqlite3の exec() を利用し、セミコロン区切りの複数文・コメントを処理する。
+   */
+  exec(sql: string): void {
+    this.db.exec(sql);
+  }
+
+  /**
+   * トランザクション内でコールバックを実行する
+   */
+  transaction<T>(callback: () => T): T {
+    const tx = this.db.transaction(callback);
+    return tx();
+  }
+
+  /**
+   * DB接続を閉じる
+   */
+  close(): void {
+    this.db.close();
+  }
+}
+
+let instance: SqliteDatabase | null = null;
+
+/**
+ * シングルトンのDB接続を取得する。
+ * dbPathは process.env.SQLITE_PATH ?? "./data/app.db"
+ */
+export function getDb(): SqliteDatabase {
+  if (!instance) {
+    const dbPath = process.env.SQLITE_PATH ?? './data/app.db';
+    instance = new SqliteDatabase(dbPath);
+  }
+
+  return instance;
+}
+
+/**
+ * テスト用途: シングルトンインスタンスをリセットする
+ */
+export function resetDbInstance(): void {
+  if (instance) {
+    instance.close();
+    instance = null;
+  }
+}
diff --git a/lib/types/index.ts b/lib/types/index.ts
new file mode 100644
index 0000000..bff64f4
--- /dev/null
+++ b/lib/types/index.ts
@@ -0,0 +1,241 @@
+/**
+ * 全Entity型定義・共有型
+ * functional-design.md のデータモデルに対応。
+ * タイムスタンプはISO8601文字列(TEXT)。真偽値はINTEGER(0/1)。
+ */
+
+// ===== 列挙型 =====
+
+export type UserRole = 'system_admin' | 'project_admin' | 'member' | 'guest';
+export type UserStatus = 'active' | 'inactive';
+export type ProjectStatus = 'active' | 'on_hold' | 'completed' | 'archived';
+export type ProjectMemberRole = 'admin' | 'member' | 'guest';
+export type BoardCategory =
+  | 'notice'
+  | 'spec'
+  | 'minutes'
+  | 'question'
+  | 'decision'
+  | 'trouble'
+  | 'memo';
+export type TodoPriority = 'low' | 'normal' | 'high';
+export type MilestoneStatus = 'open' | 'closed';
+export type CalendarEventType =
+  | 'meeting'
+  | 'deadline'
+  | 'milestone'
+  | 'todo'
+  | 'reminder'
+  | 'custom';
+export type MeetingMemberStatus = 'invited' | 'accepted' | 'declined';
+export type NotificationType =
+  | 'mention'
+  | 'todo_assigned'
+  | 'todo_due_soon'
+  | 'meeting_invited'
+  | 'board_commented'
+  | 'project_added'
+  | 'file_shared'
+  | 'note_updated';
+
+// ===== エンティティ =====
+
+export interface User {
+  id: number;
+  name: string;
+  email: string;
+  passwordHash: string | null;
+  avatarUrl: string | null;
+  role: UserRole;
+  status: UserStatus;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface Project {
+  id: number;
+  name: string;
+  description: string | null;
+  status: ProjectStatus;
+  ownerId: number;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface ProjectMember {
+  id: number;
+  projectId: number;
+  userId: number;
+  role: ProjectMemberRole;
+  joinedAt: string;
+}
+
+export interface BoardThread {
+  id: number;
+  projectId: number;
+  title: string;
+  bodyMd: string;
+  authorId: number;
+  category: BoardCategory | null;
+  isPinned: number;
+  isImportant: number;
+  createdAt: string;
+  updatedAt: string;
+  deletedAt: string | null;
+}
+
+export interface BoardComment {
+  id: number;
+  threadId: number;
+  authorId: number;
+  bodyMd: string;
+  createdAt: string;
+  updatedAt: string;
+  deletedAt: string | null;
+}
+
+export interface ChatMessage {
+  id: number;
+  projectId: number;
+  authorId: number;
+  body: string;
+  createdAt: string;
+  updatedAt: string;
+  deletedAt: string | null;
+}
+
+export interface TodoColumn {
+  id: number;
+  projectId: number;
+  name: string;
+  orderIndex: number;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface TodoItem {
+  id: number;
+  projectId: number;
+  columnId: number;
+  title: string;
+  description: string | null;
+  assigneeId: number | null;
+  creatorId: number;
+  priority: TodoPriority;
+  startDate: string | null;
+  dueDate: string | null;
+  completedAt: string | null;
+  orderIndex: number;
+  milestoneId: number | null;
+  createdAt: string;
+  updatedAt: string;
+  deletedAt: string | null;
+}
+
+export interface FileAsset {
+  id: number;
+  projectId: number;
+  uploaderId: number;
+  filename: string;
+  originalName: string;
+  mimeType: string;
+  size: number;
+  path: string;
+  createdAt: string;
+  deletedAt: string | null;
+}
+
+export interface ProjectNote {
+  id: number;
+  projectId: number;
+  title: string;
+  bodyMd: string;
+  tags: string | null;
+  isPinned: number;
+  createdById: number;
+  updatedById: number;
+  createdAt: string;
+  updatedAt: string;
+  deletedAt: string | null;
+}
+
+export interface Milestone {
+  id: number;
+  projectId: number;
+  title: string;
+  description: string | null;
+  dueDate: string | null;
+  status: MilestoneStatus;
+  createdAt: string;
+  updatedAt: string;
+  deletedAt: string | null;
+}
+
+export interface CalendarEvent {
+  id: number;
+  projectId: number;
+  title: string;
+  description: string | null;
+  type: CalendarEventType;
+  startAt: string;
+  endAt: string | null;
+  createdById: number;
+  relatedTodoId: number | null;
+  relatedMilestoneId: number | null;
+  relatedMeetingId: number | null;
+  createdAt: string;
+  updatedAt: string;
+  deletedAt: string | null;
+}
+
+export interface Meeting {
+  id: number;
+  projectId: number;
+  title: string;
+  description: string | null;
+  location: string | null;
+  meetingUrl: string | null;
+  startAt: string;
+  endAt: string;
+  agendaMd: string | null;
+  minutesMd: string | null;
+  createdById: number;
+  createdAt: string;
+  updatedAt: string;
+  deletedAt: string | null;
+}
+
+export interface MeetingMember {
+  id: number;
+  meetingId: number;
+  userId: number;
+  status: MeetingMemberStatus;
+}
+
+export interface Notification {
+  id: number;
+  userId: number;
+  projectId: number | null;
+  type: NotificationType;
+  title: string;
+  body: string | null;
+  readAt: string | null;
+  createdAt: string;
+}
+
+export interface ActivityLog {
+  id: number;
+  projectId: number;
+  actorId: number;
+  action: string;
+  targetType: string;
+  targetId: number | null;
+  metadataJson: string | null;
+  createdAt: string;
+}
+
+export interface SchemaMigration {
+  id: number;
+  filename: string;
+  appliedAt: string;
+}
diff --git a/package-lock.json b/package-lock.json
index b2642d9..d5cdd16 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -133,7 +133,6 @@
       "dev": true,
       "license": "MIT",
       "optional": true,
-      "peer": true,
       "dependencies": {
         "@emnapi/wasi-threads": "1.2.1",
         "tslib": "^2.4.0"
@@ -145,7 +144,6 @@
       "integrity": "sha512-vgj7R3y3Wgx24IQaGPA/R6YFXLHVMOZ0uVEyIQPaWs+rd1AzfEMXlAC22FYwO1XkKR6NPsq7mUandH8oIRdZFw==",
       "license": "MIT",
       "optional": true,
-      "peer": true,
       "dependencies": {
         "tslib": "^2.4.0"
       }
@@ -1643,7 +1641,6 @@
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       "devOptional": true,
       "license": "Apache-2.0",
-      "peer": true,
       "dependencies": {
         "playwright": "1.61.1"
       },
@@ -2142,7 +2139,6 @@
       "resolved": "https://registry.npmjs.org/@types/react/-/react-19.2.17.tgz",
       "integrity": "sha512-MXfmqaVPEVgkBT/aY0aGCkRWWtByiYQXo3xdQ8r5RzuFrPiRn8Gar2tQdXSUQ2GKV3bkXckek89V8wQBY2Q/Aw==",
       "license": "MIT",
-      "peer": true,
       "dependencies": {
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       }
@@ -2208,7 +2204,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
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         "@typescript-eslint/types": "8.62.0",
@@ -2913,7 +2908,6 @@
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       "license": "MIT",
-      "peer": true,
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         "@vitest/utils": "2.1.9",
         "fflate": "^0.8.2",
@@ -2957,7 +2951,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "bin": {
         "acorn": "bin/acorn"
       },
@@ -3524,7 +3517,6 @@
         }
       ],
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "baseline-browser-mapping": "^2.10.38",
         "caniuse-lite": "^1.0.30001799",
@@ -4511,7 +4503,6 @@
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-      "peer": true,
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@@ -6497,7 +6488,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "bin": {
         "jiti": "bin/jiti.js"
       }
@@ -8637,7 +8627,6 @@
         }
       ],
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "nanoid": "^3.3.12",
         "picocolors": "^1.1.1",
@@ -8948,7 +8937,6 @@
       "resolved": "https://registry.npmjs.org/react/-/react-19.2.7.tgz",
       "integrity": "sha512-HNe9WslTbXmFK8o8cmwgAeJFSBvt1bPdHCVKtaaV+WlAN36mpT4hcRpwbf3fY56ar2oIXzsBpOAiIRHAdY0OlQ==",
       "license": "MIT",
-      "peer": true,
       "engines": {
         "node": ">=0.10.0"
       }
@@ -8958,7 +8946,6 @@
       "resolved": "https://registry.npmjs.org/react-dom/-/react-dom-19.2.7.tgz",
       "integrity": "sha512-t0BRVXvbiE/o20Hfw669rLbMCDWtYZLvmJigy2f0MxsXF+71pxhR3xOkspmsO8h3ZlNzyibAmtCa3l4lYKk6gQ==",
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "scheduler": "^0.27.0"
       },
@@ -10540,7 +10527,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "engines": {
         "node": ">=12"
       },
@@ -10672,7 +10658,6 @@
       "integrity": "sha512-X8EX+XV4QR5xCsrgxaED954zTDfY8KqlDtskKEL0cHhyS/P8b4IFOvGDQpsC9Q1XnLq915wEfwwY/zzskCtmhg==",
       "dev": true,
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "esbuild": "~0.28.0"
       },
@@ -10810,7 +10795,6 @@
       "integrity": "sha512-pXWcraxM0uxAS+tN0AG/BF2TyqmHO014Z070UsJ+pFvYuRSq8KH8DmWpnbXe0pEPDHXZV3FcAbJkijJ5oNEnWw==",
       "dev": true,
       "license": "Apache-2.0",
-      "peer": true,
       "bin": {
         "tsc": "bin/tsc",
         "tsserver": "bin/tsserver"
@@ -11603,7 +11587,6 @@
       "integrity": "sha512-MSmPM9REYqDGBI8439mA4mWhV5sKmDlBKWIYbA3lRb2PTHACE0mgKwA8yQ2xq9vxDTuk4iPrECBAEW2aoFXY0Q==",
       "dev": true,
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "@vitest/expect": "2.1.9",
         "@vitest/mocker": "2.1.9",
diff --git a/tests/helpers/db.ts b/tests/helpers/db.ts
new file mode 100644
index 0000000..72d71e7
--- /dev/null
+++ b/tests/helpers/db.ts
@@ -0,0 +1,45 @@
+import os from 'node:os';
+import fs from 'node:fs';
+import path from 'node:path';
+import { SqliteDatabase } from '@/lib/db/sqlite';
+import { Migrator } from '@/lib/db/migrator';
+
+let counter = 0;
+
+/**
+ * テスト用の一時SQLite DBを作成する。
+ * 実DB(一時ファイル)を使用し、テスト終了時に自動削除される。
+ */
+export function createTestDb(): SqliteDatabase {
+  const tmpDir = os.tmpdir();
+  const dbPath = path.join(
+    tmpDir,
+    `test-${process.pid}-${Date.now()}-${counter++}.db`
+  );
+  const db = new SqliteDatabase(dbPath);
+
+  const originalClose = db.close.bind(db);
+  db.close = () => {
+    originalClose();
+    if (fs.existsSync(dbPath)) {
+      fs.unlinkSync(dbPath);
+    }
+    const walPath = `${dbPath}-wal`;
+    const shmPath = `${dbPath}-shm`;
+    if (fs.existsSync(walPath)) fs.unlinkSync(walPath);
+    if (fs.existsSync(shmPath)) fs.unlinkSync(shmPath);
+  };
+
+  return db;
+}
+
+/**
+ * マイグレーション済みのテスト用DBを作成する
+ */
+export function createMigratedTestDb(): SqliteDatabase {
+  const db = createTestDb();
+  const migrationsDir = path.join(process.cwd(), 'lib', 'db', 'migrations');
+  const migrator = new Migrator(db, migrationsDir);
+  migrator.migrate();
+  return db;
+}
diff --git a/tests/unit/lib/db/migrator.test.ts b/tests/unit/lib/db/migrator.test.ts
new file mode 100644
index 0000000..c25f102
--- /dev/null
+++ b/tests/unit/lib/db/migrator.test.ts
@@ -0,0 +1,185 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { createTestDb } from '@/tests/helpers/db';
+import { Migrator } from '@/lib/db/migrator';
+import { SqliteDatabase } from '@/lib/db/sqlite';
+
+function createTempMigrationsDir(): string {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'migrations-'));
+}
+
+function writeMigration(dir: string, filename: string, sql: string): void {
+  fs.writeFileSync(path.join(dir, filename), sql, 'utf-8');
+}
+
+describe('Migrator', () => {
+  let db: SqliteDatabase;
+  let migrationsDir: string;
+
+  beforeEach(() => {
+    db = createTestDb();
+    migrationsDir = createTempMigrationsDir();
+  });
+
+  afterEach(() => {
+    db.close();
+    fs.rmSync(migrationsDir, { recursive: true, force: true });
+  });
+
+  it('creates the schema_migrations table', () => {
+    writeMigration(
+      migrationsDir,
+      '001_init.sql',
+      'CREATE TABLE sample (id INTEGER);'
+    );
+    const migrator = new Migrator(db, migrationsDir);
+
+    migrator.migrate();
+
+    const row = db.get<{ name: string }>(
+      "SELECT name FROM sqlite_master WHERE type='table' AND name='schema_migrations'"
+    );
+    expect(row?.name).toBe('schema_migrations');
+  });
+
+  it('applies migration files in filename order', () => {
+    writeMigration(
+      migrationsDir,
+      '002_second.sql',
+      'CREATE TABLE second (id INTEGER);'
+    );
+    writeMigration(
+      migrationsDir,
+      '001_first.sql',
+      'CREATE TABLE first (id INTEGER);'
+    );
+    const migrator = new Migrator(db, migrationsDir);
+
+    migrator.migrate();
+
+    const applied = migrator.getAppliedMigrations();
+    expect(applied.map((m) => m.filename)).toEqual([
+      '001_first.sql',
+      '002_second.sql',
+    ]);
+    expect(
+      db.get<{ name: string }>(
+        "SELECT name FROM sqlite_master WHERE name='first'"
+      )
+    ).not.toBeNull();
+    expect(
+      db.get<{ name: string }>(
+        "SELECT name FROM sqlite_master WHERE name='second'"
+      )
+    ).not.toBeNull();
+  });
+
+  it('skips already-applied migrations on subsequent runs', () => {
+    writeMigration(
+      migrationsDir,
+      '001_init.sql',
+      'CREATE TABLE sample (id INTEGER);'
+    );
+    const migrator = new Migrator(db, migrationsDir);
+
+    migrator.migrate();
+    expect(migrator.getAppliedMigrations()).toHaveLength(1);
+
+    expect(() => migrator.migrate()).not.toThrow();
+    expect(migrator.getAppliedMigrations()).toHaveLength(1);
+  });
+
+  it('rolls back and does not record a migration when its SQL fails', () => {
+    writeMigration(
+      migrationsDir,
+      '001_bad.sql',
+      'CREATE TABLE will_exist (id INTEGER); NOT A VALID STATEMENT;'
+    );
+    const migrator = new Migrator(db, migrationsDir);
+
+    expect(() => migrator.migrate()).toThrow();
+
+    expect(migrator.getAppliedMigrations()).toHaveLength(0);
+    expect(
+      db.get<{ name: string }>(
+        "SELECT name FROM sqlite_master WHERE name='will_exist'"
+      )
+    ).toBeNull();
+  });
+
+  it('returns applied migrations ordered by filename', () => {
+    writeMigration(migrationsDir, '001_a.sql', 'CREATE TABLE a (id INTEGER);');
+    writeMigration(migrationsDir, '002_b.sql', 'CREATE TABLE b (id INTEGER);');
+    const migrator = new Migrator(db, migrationsDir);
+
+    migrator.migrate();
+
+    const applied = migrator.getAppliedMigrations();
+    expect(applied).toHaveLength(2);
+    expect(applied[0].filename).toBe('001_a.sql');
+    expect(applied[1].filename).toBe('002_b.sql');
+    expect(applied[0].applied_at).toBeTruthy();
+  });
+
+  it('only reads .sql files in the migrations directory', () => {
+    writeMigration(
+      migrationsDir,
+      '001_real.sql',
+      'CREATE TABLE real_t (id INTEGER);'
+    );
+    fs.writeFileSync(path.join(migrationsDir, 'README.md'), 'not a migration');
+    const migrator = new Migrator(db, migrationsDir);
+
+    migrator.migrate();
+
+    expect(migrator.getAppliedMigrations().map((m) => m.filename)).toEqual([
+      '001_real.sql',
+    ]);
+  });
+
+  it('applies the real 001_initial.sql and creates all core tables', () => {
+    const realMigrationsDir = path.join(
+      process.cwd(),
+      'lib',
+      'db',
+      'migrations'
+    );
+    const migrator = new Migrator(db, realMigrationsDir);
+
+    migrator.migrate();
+
+    const tables = db
+      .query<{
+        name: string;
+      }>("SELECT name FROM sqlite_master WHERE type='table' ORDER BY name")
+      .map((t) => t.name);
+
+    const expectedTables = [
+      'activity_logs',
+      'board_comments',
+      'board_threads',
+      'calendar_events',
+      'chat_messages',
+      'file_assets',
+      'meeting_members',
+      'meetings',
+      'milestones',
+      'notifications',
+      'project_members',
+      'project_notes',
+      'projects',
+      'schema_migrations',
+      'todo_columns',
+      'todo_items',
+      'users',
+    ];
+    for (const table of expectedTables) {
+      expect(tables).toContain(table);
+    }
+    expect(migrator.getAppliedMigrations().map((m) => m.filename)).toEqual([
+      '001_initial.sql',
+    ]);
+  });
+});
diff --git a/tests/unit/lib/db/sqlite.test.ts b/tests/unit/lib/db/sqlite.test.ts
new file mode 100644
index 0000000..1d3d6d9
--- /dev/null
+++ b/tests/unit/lib/db/sqlite.test.ts
@@ -0,0 +1,252 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { createTestDb } from '@/tests/helpers/db';
+import { SqliteDatabase } from '@/lib/db/sqlite';
+
+describe('SqliteDatabase', () => {
+  let db: SqliteDatabase;
+
+  afterEach(() => {
+    if (db) db.close();
+  });
+
+  describe('constructor', () => {
+    it('enables WAL journal mode', () => {
+      db = createTestDb();
+      const row = db.get<{ journal_mode: string }>('PRAGMA journal_mode');
+      expect(row?.journal_mode).toBe('wal');
+    });
+
+    it('enables foreign key constraints', () => {
+      db = createTestDb();
+      const row = db.get<{ foreign_keys: number }>('PRAGMA foreign_keys');
+      expect(row?.foreign_keys).toBe(1);
+    });
+  });
+
+  describe('query', () => {
+    it('returns multiple rows', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+      db.execute("INSERT INTO items (name) VALUES ('a')");
+      db.execute("INSERT INTO items (name) VALUES ('b')");
+
+      const rows = db.query<{ id: number; name: string }>(
+        'SELECT * FROM items ORDER BY id'
+      );
+
+      expect(rows).toHaveLength(2);
+      expect(rows[0].name).toBe('a');
+      expect(rows[1].name).toBe('b');
+    });
+
+    it('returns an empty array when no rows match', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+
+      const rows = db.query<{ id: number }>('SELECT * FROM items');
+
+      expect(rows).toEqual([]);
+    });
+
+    it('binds named parameters', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+      db.execute("INSERT INTO items (name) VALUES ('target')");
+      db.execute("INSERT INTO items (name) VALUES ('other')");
+
+      const rows = db.query<{ name: string }>(
+        'SELECT * FROM items WHERE name = @name',
+        { name: 'target' }
+      );
+
+      expect(rows).toHaveLength(1);
+      expect(rows[0].name).toBe('target');
+    });
+  });
+
+  describe('get', () => {
+    it('returns a single row when found', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+      const { lastInsertRowid } = db.execute(
+        "INSERT INTO items (name) VALUES ('x')"
+      );
+
+      const row = db.get<{ id: number; name: string }>(
+        'SELECT * FROM items WHERE id = @id',
+        { id: Number(lastInsertRowid) }
+      );
+
+      expect(row).not.toBeNull();
+      expect(row?.name).toBe('x');
+    });
+
+    it('returns null when no row is found', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+
+      const row = db.get<{ id: number }>('SELECT * FROM items WHERE id = @id', {
+        id: 999,
+      });
+
+      expect(row).toBeNull();
+    });
+  });
+
+  describe('execute', () => {
+    it('returns changes and lastInsertRowid for an insert', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+
+      const result = db.execute("INSERT INTO items (name) VALUES ('a')");
+
+      expect(result.changes).toBe(1);
+      expect(Number(result.lastInsertRowid)).toBeGreaterThan(0);
+    });
+
+    it('returns the number of affected rows for an update', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+      db.execute("INSERT INTO items (name) VALUES ('a')");
+      db.execute("INSERT INTO items (name) VALUES ('b')");
+
+      const result = db.execute(
+        'UPDATE items SET name = @name WHERE name = @old',
+        { name: 'updated', old: 'a' }
+      );
+
+      expect(result.changes).toBe(1);
+    });
+
+    it('returns the number of deleted rows for a delete', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+      db.execute("INSERT INTO items (name) VALUES ('a')");
+
+      const result = db.execute('DELETE FROM items WHERE name = @name', {
+        name: 'a',
+      });
+
+      expect(result.changes).toBe(1);
+    });
+  });
+
+  describe('exec', () => {
+    it('executes multiple semicolon-separated statements', () => {
+      db = createTestDb();
+
+      db.exec(`
+        CREATE TABLE a (id INTEGER PRIMARY KEY, name TEXT NOT NULL);
+        CREATE TABLE b (id INTEGER PRIMARY KEY, value INTEGER NOT NULL);
+        INSERT INTO a (name) VALUES ('first');
+        INSERT INTO b (value) VALUES (42);
+      `);
+
+      expect(db.get<{ name: string }>('SELECT name FROM a')?.name).toBe(
+        'first'
+      );
+      expect(db.get<{ value: number }>('SELECT value FROM b')?.value).toBe(42);
+    });
+
+    it('handles SQL comments alongside statements', () => {
+      db = createTestDb();
+
+      db.exec(`
+        -- this is a comment
+        CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL);
+        /* multi-line
+           comment */
+        INSERT INTO items (name) VALUES ('x');
+      `);
+
+      expect(db.query<{ name: string }>('SELECT name FROM items')).toHaveLength(
+        1
+      );
+    });
+  });
+
+  describe('transaction', () => {
+    it('commits changes when the callback succeeds', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+
+      db.transaction(() => {
+        db.execute("INSERT INTO items (name) VALUES ('a')");
+        db.execute("INSERT INTO items (name) VALUES ('b')");
+      });
+
+      const rows = db.query<{ name: string }>(
+        'SELECT * FROM items ORDER BY id'
+      );
+      expect(rows).toHaveLength(2);
+    });
+
+    it('rolls back changes when the callback throws', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+
+      expect(() =>
+        db.transaction(() => {
+          db.execute("INSERT INTO items (name) VALUES ('a')");
+          db.execute("INSERT INTO items (name) VALUES ('b')");
+          throw new Error('boom');
+        })
+      ).toThrow('boom');
+
+      const rows = db.query<{ name: string }>('SELECT * FROM items');
+      expect(rows).toHaveLength(0);
+    });
+
+    it('returns the callback value', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+
+      const result = db.transaction(() => {
+        db.execute("INSERT INTO items (name) VALUES ('a')");
+        return 'committed';
+      });
+
+      expect(result).toBe('committed');
+    });
+  });
+
+  describe('foreign key enforcement', () => {
+    it('rejects inserts that violate a foreign key constraint', () => {
+      db = createTestDb();
+      db.execute(
+        'CREATE TABLE parents (id INTEGER PRIMARY KEY, name TEXT NOT NULL)'
+      );
+      db.execute(
+        'CREATE TABLE children (id INTEGER PRIMARY KEY, parent_id INTEGER NOT NULL, FOREIGN KEY (parent_id) REFERENCES parents(id))'
+      );
+
+      expect(() =>
+        db.execute('INSERT INTO children (parent_id) VALUES (@parentId)', {
+          parentId: 999,
+        })
+      ).toThrow();
+    });
+  });
+});