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>

packages/service_repository/lib/src/entities/service_entity.dart

@@ -1,5 +1,4 @@
 import 'package:equatable/equatable.dart';
-import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:service_repository/service_repository.dart';
 import 'package:flutter/material.dart';
 
@@ -14,7 +13,7 @@ class ServiceEntity extends Equatable {
   final double latitude;
   final double longitude;
   final String day;
-  final Timestamp createdAt;
+  final String createdAt;
   final String description;
   final TimeOfDay range1Hour1;
   final TimeOfDay range1Hour2;
@@ -54,7 +53,7 @@ class ServiceEntity extends Equatable {
       latitude: doc['latitude'] as double,
       longitude: doc['longitude'] as double,
       day: doc['day'] as String,
-      createdAt: doc['created_at'] as Timestamp,
+      createdAt: doc['created_at']?.toString() ?? DateTime.now().toIso8601String(),
       description: doc['description'] as String,
       range1Hour1: parseTimeOfDay(doc['range1_hour1'] as String),
       range1Hour2: parseTimeOfDay(doc['range1_hour2'] as String),