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>

packages/user_repository/pubspec.yaml

@@ -1,6 +1,6 @@
 name: user_repository
 description: Dart package which manages the user.
-publish_to: "none" 
+publish_to: "none"
 
 version: 1.0.11+11
 
@@ -11,8 +11,10 @@ dependencies:
   flutter:
     sdk: flutter
   equatable: ^2.0.5
+  http: ^1.1.0
+  shared_preferences: ^2.0.10
 
-  # Firebase
+  # Firebase kept for FirebaseUserRepository (legacy fallback)
   firebase_auth: ^4.17.4
   cloud_firestore: ^4.15.4
   firebase_storage: ^11.6.5