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)

lib/api/services.ts

@@ -25,6 +25,7 @@ import { MeetingService } from '@/services/MeetingService';
 import { MeetingRepository } from '@/repositories/MeetingRepository';
 import { SearchService } from '@/services/SearchService';
 import { DashboardService } from '@/services/DashboardService';
+import { BackupService } from '@/services/BackupService';
 
 /**
  * Route Handler用に各Repository/Serviceを構築するファクトリ。
@@ -168,6 +169,13 @@ export function createDashboardService(): DashboardService {
   );
 }
 
+export function createBackupService(): BackupService {
+  const dbPath = process.env.SQLITE_PATH ?? './data/app.db';
+  const uploadsDir = process.env.UPLOADS_PATH ?? './data/uploads';
+  const backupsDir = './backups';
+  return new BackupService(dbPath, uploadsDir, backupsDir);
+}
+
 export function createUserRepository(): UserRepository {
   return new UserRepository(getDb());
 }