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/screens/chat/chat_screen.dart

@@ -1,5 +1,4 @@
 import 'package:chat_repository/chat_repository.dart';
-import 'package:firebase_auth/firebase_auth.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
@@ -111,7 +110,7 @@ class _ChatScreenState extends State<ChatScreen> {
                               ),
                             ),
                             subtitle: widget.service.userId ==
-                                    FirebaseAuth.instance.currentUser!.uid
+                                    ApiUserRepository.currentUserId ?? ''
                                 ? GeneralReputation(
                                     userId: widget.service.professionalId,
                                     builder: (context, reputation) {
@@ -229,7 +228,7 @@ class _ChatScreenState extends State<ChatScreen> {
 
                                 MessageEntity message = MessageEntity(
                                   ownerId:
-                                      FirebaseAuth.instance.currentUser!.uid,
+                                      ApiUserRepository.currentUserId ?? '',
                                   content: _messageController.text.trim(),
                                   createdAt: DateTime.now(),
                                 );
@@ -272,7 +271,7 @@ class _ChatScreenState extends State<ChatScreen> {
                               }
 
                               MessageEntity message = MessageEntity(
-                                ownerId: FirebaseAuth.instance.currentUser!.uid,
+                                ownerId: ApiUserRepository.currentUserId ?? '',
                                 content: _messageController.text.trim(),
                                 createdAt: DateTime.now(),
                               );
@@ -340,7 +339,7 @@ class _ChatScreenState extends State<ChatScreen> {
   List<Widget> _messagesList(List<MessageEntity> messages) {
     return messages
         .map(
-          (e) => e.ownerId != FirebaseAuth.instance.currentUser!.uid
+          (e) => e.ownerId != ApiUserRepository.currentUserId ?? ''
               ? ListTile(
                   title: Column(
                     mainAxisAlignment: MainAxisAlignment.start,
@@ -437,12 +436,12 @@ class _ChatScreenState extends State<ChatScreen> {
 
   Future<List<dynamic>> _getUserAndProfessionalInfo(
       ServiceEntity service) async {
-    final userRepo = FirebaseUserRepository(FirebaseAuth.instance);
+    final userRepo = Injector.appInstance.get<UserRepository>();
 
     final MyUser? userInfo;
     final MyUser? myInfo;
 
-    if (FirebaseAuth.instance.currentUser!.uid == service.userId) {
+    if ((ApiUserRepository.currentUserId ?? '') == service.userId) {
       userInfo = await userRepo.getMyUser(service.professionalId);
       myInfo = await userRepo.getMyUser(service.userId);
     } else {