feat: setup barrelsby for automatic barrel file generation

Add barrelsby as a dev dependency with a `generate-barrels` npm script and a `barrelesby.json` config targeting `./src`. This automates creation of barrel/index files to simplify imports across the project.

src/data/models/chat/chat_history_response.ts

@@ -0,0 +1,60 @@
+/**
+ * 聊天历史响应
+ * 原始 Dart: ChatHistoryResponse (lib/data/models/chat/chat_response.dart)
+ *
+ * 注：原始 Dart 中 `total` 为 `int?`，按"全部非空"约定兜底为 0。
+ */
+import { ChatMessage } from "./chat_message";
+
+export class ChatHistoryResponse {
+  readonly messages: ChatMessage[];
+  readonly total: number;
+  readonly limit: number;
+  readonly offset: number;
+
+  constructor(params: {
+    messages: ChatMessage[];
+    total?: number;
+    limit: number;
+    offset: number;
+  }) {
+    this.messages = params.messages;
+    this.total = params.total ?? 0;
+    this.limit = params.limit;
+    this.offset = params.offset;
+    Object.freeze(this);
+  }
+
+  toJson(): Record<string, unknown> {
+    return {
+      messages: this.messages.map((m) => m.toJson()),
+      total: this.total,
+      limit: this.limit,
+      offset: this.offset,
+    };
+  }
+
+  static fromJson(json: Record<string, unknown>): ChatHistoryResponse {
+    const requireNumber = (key: string): number => {
+      const v = json[key];
+      if (typeof v !== "number") {
+        throw new Error(
+          `ChatHistoryResponse.${key} is required and must be a number`
+        );
+      }
+      return v;
+    };
+    const rawMessages = json.messages;
+    const messages: ChatMessage[] = Array.isArray(rawMessages)
+      ? (rawMessages as Record<string, unknown>[]).map((m) =>
+          ChatMessage.fromJson(m)
+        )
+      : [];
+    return new ChatHistoryResponse({
+      messages,
+      total: typeof json.total === "number" ? json.total : undefined,
+      limit: requireNumber("limit"),
+      offset: requireNumber("offset"),
+    });
+  }
+}