📦 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/@nodelib/fs.walk/out/index.d.ts

@@ -0,0 +1,14 @@
+/// <reference types="node" />
+import type { Readable } from 'stream';
+import type { Dirent, FileSystemAdapter } from '@nodelib/fs.scandir';
+import { AsyncCallback } from './providers/async';
+import Settings, { DeepFilterFunction, EntryFilterFunction, ErrorFilterFunction, Options } from './settings';
+import type { Entry } from './types';
+declare function walk(directory: string, callback: AsyncCallback): void;
+declare function walk(directory: string, optionsOrSettings: Options | Settings, callback: AsyncCallback): void;
+declare namespace walk {
+    function __promisify__(directory: string, optionsOrSettings?: Options | Settings): Promise<Entry[]>;
+}
+declare function walkSync(directory: string, optionsOrSettings?: Options | Settings): Entry[];
+declare function walkStream(directory: string, optionsOrSettings?: Options | Settings): Readable;
+export { walk, walkSync, walkStream, Settings, AsyncCallback, Dirent, Entry, FileSystemAdapter, Options, DeepFilterFunction, EntryFilterFunction, ErrorFilterFunction };