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/models/usuario_profesional.dart

@@ -21,12 +21,19 @@ class UsuarioProfesional {
     };
   }
 
-  // Método para deserializar desde JSON
   factory UsuarioProfesional.fromJson(Map<String, dynamic> json) {
     return UsuarioProfesional(
       user: Usuario.fromDocument(json['user']),
       professionalInfo: Profesional.fromDocument(json['professionalInfo']),
-      averageScore: json['averageScore'].toDouble(),
+      averageScore: (json['averageScore'] as num?)?.toDouble() ?? 0.0,
+    );
+  }
+
+  static UsuarioProfesional fromDocument(Map<String, dynamic> doc) {
+    return UsuarioProfesional(
+      user: Usuario.fromDocument(doc['user'] as Map<String, dynamic>),
+      professionalInfo: Profesional.fromDocument(doc['professional_info'] as Map<String, dynamic>),
+      averageScore: (doc['average_score'] as num?)?.toDouble() ?? 0.0,
     );
   }