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/profession_repository/lib/src/repositories/firebase_profession_repository.dart

@@ -1,30 +0,0 @@
-import 'dart:developer';
-
-import 'package:profession_repository/profession_repository.dart';
-import 'package:cloud_firestore/cloud_firestore.dart';
-
-class FirebaseProfessionRepository implements ProfessionRepository {
-  final professionsCollection =
-      FirebaseFirestore.instance.collection('professions');
-
-  @override
-  Future<Professions> getProfessions() async {
-    try {
-      final doc = await professionsCollection.doc("professions").get();
-      return Professions.fromDocument(doc.data() as Map<String, dynamic>);
-    } catch (e) {
-      log('Error getting documents: $e');
-      rethrow;
-    }
-  }
-}
-
-class Professions {
-  final List<String> professions;
-
-  Professions(this.professions);
-
-  factory Professions.fromDocument(Map<String, dynamic> json) {
-    return Professions(List<String>.from(json['professions']));
-  }
-}