📦 添加虚拟环境和启动脚本

新增:
- backend/venv/ - Python 虚拟环境
- backend/start.sh - 启动脚本（使用虚拟环境）
- backend/requirements.txt - 依赖列表
- .gitignore - 忽略虚拟环境和缓存文件

说明:
- 每个项目使用独立虚拟环境
- 避免依赖冲突
- 启动脚本自动创建和激活虚拟环境

frontend/node_modules/memfs/lib/Dirent.d.ts

@@ -0,0 +1,19 @@
+import { Link } from './node';
+import { TEncodingExtended, TDataOut } from './encoding';
+/**
+ * A directory entry, like `fs.Dirent`.
+ */
+export declare class Dirent {
+    static build(link: Link, encoding: TEncodingExtended | undefined): Dirent;
+    name: TDataOut;
+    private mode;
+    private _checkModeProperty;
+    isDirectory(): boolean;
+    isFile(): boolean;
+    isBlockDevice(): boolean;
+    isCharacterDevice(): boolean;
+    isSymbolicLink(): boolean;
+    isFIFO(): boolean;
+    isSocket(): boolean;
+}
+export default Dirent;