feat:增加消息记录功能

lib/models/chat_session.dart

@@ -0,0 +1,30 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'chat_session.g.dart';
+
+@JsonSerializable()
+class ChatSession {
+  final int conversationId;
+  final int targetUserId;
+  final String title;
+  final String avatarUrl;
+  final int msgType;
+  final String lastMessageContent;
+  final DateTime lastMessageTime;
+  final int unreadCount;
+
+  ChatSession({
+    required this.conversationId,
+    required this.targetUserId,
+    required this.title,
+    required this.avatarUrl,
+    required this.msgType,
+    required this.lastMessageContent,
+    required this.lastMessageTime,
+    required this.unreadCount,
+  });
+
+  factory ChatSession.fromJson(Map<String, dynamic> json) => _$ChatSessionFromJson(json);
+
+  Map<String, dynamic> toJson() => _$ChatSessionToJson(this);
+}