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/providers/professions_provider.dart

@@ -1,13 +1,11 @@
 import 'package:flutter/material.dart';
-import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:prosapp_web_app/models/profession.dart';
+import 'package:prosapp_web_app/services/api_service.dart';
 
 class ProfessionsProvider extends ChangeNotifier {
   List<Profession> professions = [];
   bool isLoading = true;
-
-  final _professionsCollection =
-      FirebaseFirestore.instance.collection('professions');
+  final _api = ApiService.instance;
 
   ProfessionsProvider() {
     getProfessions();
@@ -15,14 +13,14 @@ class ProfessionsProvider extends ChangeNotifier {
 
   getProfessions() async {
     try {
-      final documentSnapshot =
-          await _professionsCollection.doc('professions').get();
-
-      final data = documentSnapshot.data() as Map<String, dynamic>;
-
-      professions = (data['professions'] as List<dynamic>)
-          .map((item) => Profession(name: item as String))
-          .toList();
+      final data = await _api.get('/professions');
+      if (data is List) {
+        professions = data.map((e) => Profession(name: e['name'] as String)).toList();
+      } else if (data is Map && data['professions'] is List) {
+        professions = (data['professions'] as List)
+            .map((e) => Profession(name: e as String))
+            .toList();
+      }
     } catch (e) {
       print('Error obteniendo profesiones: $e');
     } finally {