feat(chat): 发收消息全量实现 (#25~#28)

- 移除 @riverpod/@freezed 注解依赖，全部改为手写 Provider（无需 build_runner）
  · LoginState 改为纯 Dart，LoginViewModel/ThemeViewModel/ChatViewModel 改为 Notifier
  · UserNotifier 改为 FamilyAsyncNotifier<User?,int>，mini_app_provider 改为手写 Provider
  · 15 个 StreamProvider/StreamProvider.family 从 @riverpod 迁移至手写

- 发送消息（#25）
  · SendMessageRequest/SendMessageResponse DTO
  · SendMessageUseCase：乐观写入 DB → HTTP POST → 更新 Chat 摘要

- 接收消息 WS（#26）
  · WsMessageService：监听 mode2 WS 帧 → HTTP 补拉 → DB 写入 → Chat 更新
  · FetchHistoryRequest/FetchHistoryResponse DTO（GET /app/api/chat/history）
  · FetchHistoryUseCase：拉取 → insertOrReplaceAll

- DI 装配（chat_service_providers.dart）
  · wsMessageServiceProvider、sendMessageUseCaseProvider、fetchHistoryUseCaseProvider

- 聊天列表页（#27）
  · ChatListViewModel（Notifier<void>）+ chat_page.dart 真实会话列表 UI
  · ListTile：头像首字母、最新消息摘要、未读角标、时间格式化

- 聊天详情页（#28）
  · ChatDetailViewModel（FamilyNotifier<ChatDetailState,int>）+ chat_detail_page.dart
  · 消息气泡（自己/他人分左右）、底部输入框、发送状态与错误提示

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

apps/im_app/lib/core/services/ws_message_service.dart

@@ -0,0 +1,135 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:networks_sdk/networks_sdk.dart';
+
+import 'package:im_app/core/services/socket_manager.dart';
+import 'package:im_app/data/remote/fetch_history_request.dart';
+import 'package:im_app/domain/repositories/chat_repository.dart';
+import 'package:im_app/domain/repositories/message_repository.dart';
+
+/// WS 实时消息接收服务
+///
+/// 监听 [SocketManager.messageStream]，解析 mode2 协议帧：
+/// ```json
+/// {
+///   "chat": { "r": [{ "id": <chatId>, "msg_idx": N, "typ": N, "last_msg": "..." }] },
+///   "message_realtime_pb": <bytes>
+/// }
+/// ```
+///
+/// 每帧含 `chat.r` 时，通过 HTTP GET `/app/api/chat/history` 拉取完整消息内容，
+/// 写入 [MessageRepository]，再更新 [ChatRepository] 的 lastMsg。
+/// UI 层通过 `StreamProvider` 监听 DB 变化自动更新，无需额外信令。
+///
+/// ## 生命周期
+///
+/// 由 [WsMessageServiceProvider] 管理，登录后随 SocketManager 一同启动，
+/// 登出时 Provider dispose 触发 [stop]。
+class WsMessageService {
+  final SocketManager _socketManager;
+  final NetworksSdkApi _apiClient;
+  final MessageRepository _messageRepo;
+  final ChatRepository _chatRepo;
+
+  StreamSubscription<Map<String, dynamic>>? _sub;
+
+  WsMessageService({
+    required SocketManager socketManager,
+    required NetworksSdkApi apiClient,
+    required MessageRepository messageRepo,
+    required ChatRepository chatRepo,
+  })  : _socketManager = socketManager,
+        _apiClient = apiClient,
+        _messageRepo = messageRepo,
+        _chatRepo = chatRepo;
+
+  // ── 生命周期 ──────────────────────────────────────────────────────────────
+
+  void start() {
+    _sub?.cancel();
+    _sub = _socketManager.messageStream.listen(
+      _handleFrame,
+      onError: (e) => debugPrint('[WsMessageService] stream error: $e'),
+    );
+    debugPrint('[WsMessageService] started');
+  }
+
+  void stop() {
+    _sub?.cancel();
+    _sub = null;
+    debugPrint('[WsMessageService] stopped');
+  }
+
+  // ── 帧处理 ────────────────────────────────────────────────────────────────
+
+  Future<void> _handleFrame(Map<String, dynamic> frame) async {
+    try {
+      final chatPayload = frame['chat'] as Map<String, dynamic>?;
+      if (chatPayload == null) return;
+
+      final rList = chatPayload['r'] as List<dynamic>?;
+      if (rList == null || rList.isEmpty) return;
+
+      for (final item in rList) {
+        final entry = item as Map<String, dynamic>?;
+        if (entry == null) continue;
+
+        final chatId = (entry['id'] as num?)?.toInt();
+        final msgIdx = (entry['msg_idx'] as num?)?.toInt();
+        if (chatId == null || msgIdx == null) continue;
+
+        await _fetchAndSaveMessages(chatId: chatId, anchorIdx: msgIdx);
+        await _updateChatMeta(chatId: chatId, entry: entry);
+      }
+    } catch (e, st) {
+      debugPrint('[WsMessageService] _handleFrame error: $e\n$st');
+    }
+  }
+
+  /// 通过 HTTP 拉取消息并写入 DB
+  Future<void> _fetchAndSaveMessages({
+    required int chatId,
+    required int anchorIdx,
+  }) async {
+    try {
+      final response = await _apiClient.executeRequest(
+        FetchHistoryRequest(chatId: chatId, chatIdx: anchorIdx, limit: 20),
+      );
+      if (response == null || response.messages.isEmpty) return;
+
+      final entities = response.messages.map((m) => m.toEntity()).toList();
+      await _messageRepo.insertOrReplaceAll(entities);
+      debugPrint(
+        '[WsMessageService] saved ${entities.length} messages for chat $chatId',
+      );
+    } catch (e) {
+      debugPrint('[WsMessageService] fetch error for chat $chatId: $e');
+    }
+  }
+
+  /// 更新聊天列表中对应 Chat 的 lastMsg / lastTyp / msgIdx
+  Future<void> _updateChatMeta({
+    required int chatId,
+    required Map<String, dynamic> entry,
+  }) async {
+    try {
+      final existing = await _chatRepo.getChat(chatId);
+      if (existing == null) return;
+
+      final lastMsg = entry['last_msg'] as String?;
+      final lastTyp = (entry['typ'] as num?)?.toInt();
+      final msgIdx = (entry['msg_idx'] as num?)?.toInt();
+
+      await _chatRepo.updateChat(
+        existing.copyWith(
+          lastMsg: lastMsg ?? existing.lastMsg,
+          lastTyp: lastTyp ?? existing.lastTyp,
+          msgIdx: msgIdx ?? existing.msgIdx,
+        ),
+      );
+    } catch (e) {
+      debugPrint('[WsMessageService] updateChatMeta error: $e');
+    }
+  }
+}