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/data/remote/send_message_request.dart

@@ -0,0 +1,88 @@
+import 'package:networks_sdk/networks_sdk.dart';
+
+import 'package:im_app/core/foundation/api_paths.dart';
+import 'package:im_app/domain/entities/message.dart';
+
+// ── 发送消息响应 ───────────────────────────────────────────────────────────────
+
+/// 发送消息接口响应
+class SendMessageResponse {
+  final int messageId;
+  final int chatIdx;
+  final int sendTime;
+
+  const SendMessageResponse({
+    required this.messageId,
+    required this.chatIdx,
+    required this.sendTime,
+  });
+
+  factory SendMessageResponse.fromJson(Map<String, dynamic> json) =>
+      SendMessageResponse(
+        messageId:
+            (json['message_id'] ?? json['messageId'] ?? json['id'] ?? 0)
+                as int,
+        chatIdx:
+            (json['chat_idx'] ?? json['chatIdx'] ?? 0) as int,
+        sendTime:
+            (json['send_time'] ?? json['sendTime'] ?? 0) as int,
+      );
+
+  Message toEntity({
+    required int chatId,
+    required int sendId,
+    required String content,
+    required int typ,
+  }) =>
+      Message(
+        id: 0,
+        messageId: messageId,
+        chatId: chatId,
+        chatIdx: chatIdx,
+        sendId: sendId,
+        content: content,
+        typ: typ,
+        sendTime: sendTime,
+      );
+}
+
+// ── 发送消息请求 ───────────────────────────────────────────────────────────────
+
+/// POST /app/api/chat/send-message — 发送文本消息
+///
+/// [typ] 消息类型：1 = 文本，详见服务端 MessageType 枚举。
+/// [sendTime] Unix 时间戳（秒），由客户端生成，用于服务端去重。
+class SendMessageRequest extends ApiRequestable<SendMessageResponse> {
+  final int chatId;
+  final String content;
+  final int typ;
+  final int sendTime;
+
+  const SendMessageRequest({
+    required this.chatId,
+    required this.content,
+    required this.typ,
+    required this.sendTime,
+  });
+
+  @override
+  String get path => ApiPaths.chatSendMessage;
+
+  @override
+  HttpMethod get method => HttpMethod.post;
+
+  @override
+  Map<String, dynamic> get parameters => {
+        'chat_id': chatId,
+        'content': content,
+        'typ': typ,
+        'send_time': sendTime,
+      };
+
+  @override
+  SendMessageResponse? decodeResponse(dynamic response) {
+    final data = (response as dynamic).data;
+    if (data is! Map<String, dynamic>) return null;
+    return SendMessageResponse.fromJson(data);
+  }
+}