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/components/settings/BackupSettingsPageClient.tsx

@@ -2,7 +2,7 @@
 
 import { useState, useEffect } from 'react';
 import { backupClient, BackupListResponse } from '@/clients/backup-client';
-import { BackupConfig } from '@/services/backup';
+import { BackupConfig } from '@/services/data-management/backup';
 import { Button } from '@/components/ui/Button';
 import { Card, CardHeader, CardContent } from '@/components/ui/Card';
 import { Input } from '@/components/ui/Input';