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/recent_memory.ts

@@ -0,0 +1,59 @@
+/**
+ * 最近记忆模型
+ * 原始 Dart: RecentMemory (lib/data/models/user/recent_memory.dart)
+ *
+ * 注：原始 Dart 中 `createdAt` 为 `String?`，按"全部非空"约定兜底为空串。
+ */
+export class RecentMemory {
+  readonly type: string;
+  readonly content: string;
+  readonly importance: number;
+  readonly createdAt: string;
+
+  constructor(params: {
+    type: string;
+    content: string;
+    importance: number;
+    createdAt?: string;
+  }) {
+    this.type = params.type;
+    this.content = params.content;
+    this.importance = params.importance;
+    this.createdAt = params.createdAt ?? "";
+    Object.freeze(this);
+  }
+
+  toJson(): Record<string, unknown> {
+    return {
+      type: this.type,
+      content: this.content,
+      importance: this.importance,
+      createdAt: this.createdAt,
+    };
+  }
+
+  static fromJson(json: Record<string, unknown>): RecentMemory {
+    const requireString = (key: string): string => {
+      const v = json[key];
+      if (typeof v !== "string") {
+        throw new Error(
+          `RecentMemory.${key} is required and must be a string`
+        );
+      }
+      return v;
+    };
+    const importance = json.importance;
+    if (typeof importance !== "number") {
+      throw new Error(
+        "RecentMemory.importance is required and must be a number"
+      );
+    }
+    return new RecentMemory({
+      type: requireString("type"),
+      content: requireString("content"),
+      importance,
+      createdAt:
+        typeof json.createdAt === "string" ? json.createdAt : undefined,
+    });
+  }
+}