feat: refactor service organization and update imports

- Introduced a new structure for services in `src/services/` to improve organization by domain, including core, analytics, data management, integrations, and task management.
- Moved relevant files to their new locations and updated all internal and external imports accordingly.
- Updated `TODO.md` to reflect the new service organization and outlined phases for further refactoring.

src/app/api/user-preferences/route.ts

@@ -1,5 +1,5 @@
 import { NextRequest, NextResponse } from 'next/server';
-import { userPreferencesService } from '@/services/user-preferences';
+import { userPreferencesService } from '@/services/core/user-preferences';
 
 /**
  * GET /api/user-preferences - Récupère toutes les préférences utilisateur