feat: migrate prosappco from Firebase to NestJS REST API (Fase 2)

- Replace all Firebase* repositories with Api* repositories using HTTP + SharedPreferences JWT
- Remove Firebase.initializeApp() and firebase_messaging background handler from main.dart
- Update DI (app_di.dart) to inject Api* repositories instead of Firebase* ones
- Replace all Timestamp/cloud_firestore usage with ISO 8601 String dates
- Stub PhoneVerificationService (Firebase phone OTP → backend OTP when implemented)
- Add ApiService singleton with JWT management in lib/services/
- Legacy firebase_*_repository.dart files preserved for Fase 4 cleanup

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/blocs/service_bloc/service_event.dart

@@ -117,7 +117,7 @@ class CreateService extends ServiceEvent {
   final double latitude;
   final double longitude;
   final String day;
-  final Timestamp createdAt;
+  final String createdAt;
   final String description;
   final TimeOfDay range1Hour1;
   final TimeOfDay range1Hour2;