feat: migrate Firebase → NestJS REST API backend

Replace all Firebase SDK (Auth, Firestore, Storage) with HTTP calls
to backend.prosapp.co/api/v1:

- New ApiService singleton (JWT token, GET/POST/PATCH/DELETE/upload)
- auth_provider: Firebase Auth → /auth/login, /auth/register, /auth/phone/*
- services_provider + calendar_services_provider → /services endpoints
- professional_provider + professionals_provider → /professional-info, /users/professionals
- profile_form_provider + professional_form_provider → /users/me, /storage/upload
- cities/professions/settings providers → /cities, /professions, /settings
- firebase_chat_repository → polling via /chats endpoints (3s interval)
- firebase_score_repository → polling via /comments endpoints (10s interval)
- professional_detail_provider → /users/:id + /professional-info/:id
- dashboard_view: Firestore.add → POST /services
- chat_view + rating_view: FirebaseAuth.uid → AuthProvider.user.id
- Models: Timestamp → String for createdAt fields
- google_fonts upgraded to ^8.1.0 (Dart 3.12 compat)
- Remove firebase_core, firebase_auth, cloud_firestore, firebase_storage from pubspec

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

lib/ui/views/phone_view.dart

@@ -77,7 +77,7 @@ class PhoneView extends StatelessWidget {
                                         showDialog(
                                           context: context,
                                           builder: (context) => _buildOtpModal(
-                                              context, authProvider),
+                                              context, authProvider, phoneFormProvider.phone),
                                         );
                                       }
                                     },
@@ -102,7 +102,7 @@ class PhoneView extends StatelessWidget {
     );
   }
 
-  Widget _buildOtpModal(BuildContext context, AuthProvider authProvider) {
+  Widget _buildOtpModal(BuildContext context, AuthProvider authProvider, String phone) {
     final _otpController = TextEditingController();
 
     return AlertDialog(
@@ -124,7 +124,7 @@ class PhoneView extends StatelessWidget {
             final otp = _otpController.text.trim();
 
             if (otp.isNotEmpty) {
-              await authProvider.linkPhoneWithOTP(otp);
+              await authProvider.linkPhoneWithOTP(phone, otp);
               Navigator.of(context).pop();
             } else {
               ScaffoldMessenger.of(context).showSnackBar(