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/chat_repository/lib/src/repositories/firebase_chat_repository.dart

@@ -1,43 +0,0 @@
-import 'dart:developer';
-
-import 'package:chat_repository/chat_repository.dart';
-import 'package:cloud_firestore/cloud_firestore.dart';
-
-class FirebaseChatRepository {
-  final chatCollection = FirebaseFirestore.instance.collection('chats');
-
-  Stream<ChatEntity?> getChatById(String chatId) {
-    return chatCollection.doc(chatId).snapshots().map((snapshot) {
-      try {
-        if (snapshot.exists) {
-          return ChatEntity.fromDocument(snapshot.data()!);
-        } else {
-          return null;
-        }
-      } catch (e) {
-        log(e.toString());
-        return null;
-      }
-    });
-  }
-
-  Future<ChatEntity> createNewChat(
-      String chatId, String userId, String professionalId) async {
-    ChatEntity chat = ChatEntity(
-      id: chatId,
-      userId: userId,
-      professionalId: professionalId,
-      messages: const [],
-    );
-
-    await chatCollection.doc(chatId).set(chat.toDocument());
-
-    return chat;
-  }
-
-  sendMessage(String chatId, MessageEntity message) {
-    chatCollection.doc(chatId).update({
-      'messages': FieldValue.arrayUnion([message.toDocument()])
-    });
-  }
-}