📦 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/index.d.ts

@@ -0,0 +1,21 @@
+import Stats from './Stats';
+import Dirent from './Dirent';
+import { Volume as _Volume, StatWatcher, FSWatcher, IReadStream, IWriteStream, DirectoryJSON } from './volume';
+import { IPromisesAPI } from './promises';
+import { constants } from './constants';
+export { DirectoryJSON };
+export declare const Volume: typeof _Volume;
+export declare const vol: _Volume;
+export interface IFs extends _Volume {
+    constants: typeof constants;
+    Stats: new (...args: any[]) => Stats;
+    Dirent: new (...args: any[]) => Dirent;
+    StatWatcher: new () => StatWatcher;
+    FSWatcher: new () => FSWatcher;
+    ReadStream: new (...args: any[]) => IReadStream;
+    WriteStream: new (...args: any[]) => IWriteStream;
+    promises: IPromisesAPI;
+    _toUnixTimestamp: any;
+}
+export declare function createFsFromVolume(vol: _Volume): IFs;
+export declare const fs: IFs;