feat(m2): DB foundation tests + multi-statement migration fix

- Add SqliteDatabase.exec() using better-sqlite3 exec() so the migrator
  can run multi-statement SQL files (prepare() rejected 001_initial.sql)
- Migrator now uses exec() for migration file content
- Fix tests/helpers/db.ts: replace CJS require() with ESM import
- Add unit tests for SqliteDatabase (query/get/execute/transaction/exec,
  WAL & foreign_keys pragmas) and Migrator (ordering, idempotency,
  rollback, real 001_initial.sql applies)
- Restore .gitignore steering exclusion; remove stale steering files

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',
+    ]);
+  });
+});