chore: remove Firebase dependencies and legacy code (Fase 4)

- Delete all firebase_*_repository.dart files (replaced by api_* equivalents)
- Remove cloud_firestore, firebase_auth, firebase_storage, firebase_core from all package pubspecs
- Remove cloud_firestore from main pubspec.yaml
- Delete firebase_options.dart (no longer referenced)

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

packages/city_repository/lib/src/repositories/firebase_city_repository.dart

@@ -1,44 +0,0 @@
-import 'dart:developer';
-
-import 'package:city_repository/city_repository.dart';
-import 'package:cloud_firestore/cloud_firestore.dart';
-
-class FirebaseCityRepository implements CityRepository {
-  final citiesCollection = FirebaseFirestore.instance.collection('countries v2');
-
-  List<CityUi>? _cities;
-
-  @override
-  Future<List<CityUi>> getCities() async {
-    if (_cities != null) {
-      return _cities!;
-    }
-
-    final List<CityUi> cities = [];
-
-    try {
-      final doc = await citiesCollection.doc("Colombia").get();
-
-      final data = doc.data();
-
-      final country = CountryEntity.fromDocument(data as Map<String, dynamic>);
-
-      for (var region in country.regions) {
-        for (var city in region.cities) {
-          cities.add(CityUi(
-            cityName: city.name,
-            coordsOfCity: city.coords,
-            stateOfCity: region.name,
-            countryOfCity: country.name,
-          ));
-        }
-      }
-    } catch (e) {
-      log(e.toString());
-      rethrow;
-    }
-
-    _cities = cities;
-    return cities;
-  }
-}