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/constansts.dart

@@ -1,5 +1,7 @@
 const String GOOGLE_MAPS_API_KEY = 'AIzaSyCW_og6qQ8W8G-5_BxIS4sBnl8cLkjL95s';
 
+const String API_BASE_URL = String.fromEnvironment('API_BASE_URL', defaultValue: 'http://localhost:3000/api/v1');
+
 const String MAP_STYLE = '''
     [
   {