feat: complete Phase 3 of service refactoring

- Marked tasks in `TODO.md` as completed for moving backup-related files to the `data-management` directory and correcting imports across the codebase.
- Updated imports in `backup-manager.ts`, API routes, and various components to reflect the new structure.
- Removed obsolete `backup.ts` and `backup-scheduler.ts` files to streamline the codebase.
- Added new tasks in `TODO.md` for future cleaning and organization of service imports.

src/clients/backup-client.ts

@@ -1,5 +1,5 @@
 import { httpClient } from './base/http-client';
-import { BackupInfo, BackupConfig } from '@/services/backup';
+import { BackupInfo, BackupConfig } from '@/services/data-management/backup';
 
 export interface BackupListResponse {
   backups: BackupInfo[];