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/stt_data.ts

@@ -0,0 +1,24 @@
+/**
+ * STT（语音转文字）响应
+ * 原始 Dart: SttData (lib/data/models/chat/stt_response.dart)
+ */
+export class SttData {
+  readonly text: string;
+
+  constructor(params: { text: string }) {
+    this.text = params.text;
+    Object.freeze(this);
+  }
+
+  toJson(): Record<string, unknown> {
+    return { text: this.text };
+  }
+
+  static fromJson(json: Record<string, unknown>): SttData {
+    const text = json.text;
+    if (typeof text !== "string") {
+      throw new Error("SttData.text is required and must be a string");
+    }
+    return new SttData({ text });
+  }
+}