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/user/avatar_data.ts

@@ -0,0 +1,35 @@
+/**
+ * 头像数据模型 - 对应后端 AvatarData schema
+ * 原始 Dart: AvatarData (lib/data/models/user/user.dart)
+ *
+ * 注：原始 Dart 中 `avatarUrl` 为 `String?`，按"全部非空"约定兜底为空串。
+ */
+export class AvatarData {
+  readonly avatarUrl: string;
+  readonly userId: string;
+
+  constructor(params: { avatarUrl?: string; userId: string }) {
+    this.avatarUrl = params.avatarUrl ?? "";
+    this.userId = params.userId;
+    Object.freeze(this);
+  }
+
+  toJson(): Record<string, unknown> {
+    return {
+      avatarUrl: this.avatarUrl,
+      userId: this.userId,
+    };
+  }
+
+  static fromJson(json: Record<string, unknown>): AvatarData {
+    const userId = json.userId;
+    if (typeof userId !== "string") {
+      throw new Error("AvatarData.userId is required and must be a string");
+    }
+    return new AvatarData({
+      userId,
+      avatarUrl:
+        typeof json.avatarUrl === "string" ? json.avatarUrl : undefined,
+    });
+  }
+}