feat(m14): backup & admin (zip via fflate, admin guard, tests, e2e)

- BackupService (admin-only: createBackup zips DB+uploads via fflate to
  backups/backup-<ts>.zip, listBackups newest-first, getBackupPath with
  path-traversal guard)
- Admin backup APIs: GET/POST /api/admin/backups, GET /api/admin/backups/:filename
- Admin backups screen (admin-only) + BackupCreateButton
- Playwright globalSetup seeds a system_admin user for admin E2E
- add fflate dependency
- Unit tests (BackupService: zip content, list, admin guard, traversal) +
  e2e backup (create/list/download + non-admin 403)

tests/unit/services/BackupService.test.ts

@@ -0,0 +1,81 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { unzipSync } from 'fflate';
+import { BackupService } from '@/services/BackupService';
+import { ForbiddenError, NotFoundError } from '@/lib/errors';
+
+describe('BackupService', () => {
+  let root: string;
+  let dbPath: string;
+  let uploadsDir: string;
+  let backupsDir: string;
+  let service: BackupService;
+
+  beforeEach(() => {
+    root = fs.mkdtempSync(path.join(os.tmpdir(), 'backup-'));
+    dbPath = path.join(root, 'app.db');
+    uploadsDir = path.join(root, 'uploads');
+    backupsDir = path.join(root, 'backups');
+    fs.writeFileSync(dbPath, Buffer.from('fake-db-content'));
+    fs.mkdirSync(uploadsDir, { recursive: true });
+    fs.writeFileSync(path.join(uploadsDir, 'a.txt'), Buffer.from('hello'));
+    fs.mkdirSync(path.join(uploadsDir, 'sub'), { recursive: true });
+    fs.writeFileSync(
+      path.join(uploadsDir, 'sub', 'b.txt'),
+      Buffer.from('world')
+    );
+    service = new BackupService(dbPath, uploadsDir, backupsDir);
+  });
+
+  afterEach(() => {
+    fs.rmSync(root, { recursive: true, force: true });
+  });
+
+  const admin = { id: 1, role: 'system_admin' as const };
+  const member = { id: 2, role: 'member' as const };
+
+  it('createBackup zips DB + uploads into backups dir', () => {
+    const backup = service.createBackup(admin);
+    expect(backup.filename).toMatch(/^backup-.+\.zip$/);
+    const fullPath = path.join(backupsDir, backup.filename);
+    expect(fs.existsSync(fullPath)).toBe(true);
+    expect(backup.size).toBeGreaterThan(0);
+
+    // ZIP内容を検証
+    const zip = new Uint8Array(fs.readFileSync(fullPath));
+    const unzipped = unzipSync(zip);
+    expect(Object.keys(unzipped)).toContain('app.db');
+    expect(Object.keys(unzipped)).toContain('uploads/a.txt');
+    expect(Object.keys(unzipped)).toContain('uploads/sub/b.txt');
+  });
+
+  it('listBackups returns created backups newest first', () => {
+    service.createBackup(admin);
+    const list = service.listBackups(admin);
+    expect(list).toHaveLength(1);
+    expect(list[0].filename).toMatch(/^backup-.+\.zip$/);
+  });
+
+  it('forbids a non-admin from creating/listing', () => {
+    expect(() => service.createBackup(member)).toThrow(ForbiddenError);
+    expect(() => service.listBackups(member)).toThrow(ForbiddenError);
+  });
+
+  it('getBackupPath rejects path traversal and missing files', () => {
+    service.createBackup(admin);
+    expect(() => service.getBackupPath(admin, '../evil.zip')).toThrow(
+      NotFoundError
+    );
+    expect(() =>
+      service.getBackupPath(admin, 'backup-doesnotexist.zip')
+    ).toThrow(NotFoundError);
+  });
+
+  it('getBackupPath returns the path for a valid backup', () => {
+    const backup = service.createBackup(admin);
+    const p = service.getBackupPath(admin, backup.filename);
+    expect(fs.existsSync(p)).toBe(true);
+  });
+});