📦 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/readers/sync.d.ts

@@ -0,0 +1,15 @@
+import * as fsScandir from '@nodelib/fs.scandir';
+import type { Entry } from '../types';
+import Reader from './reader';
+export default class SyncReader extends Reader {
+    protected readonly _scandir: typeof fsScandir.scandirSync;
+    private readonly _storage;
+    private readonly _queue;
+    read(): Entry[];
+    private _pushToQueue;
+    private _handleQueue;
+    private _handleDirectory;
+    private _handleError;
+    private _handleEntry;
+    private _pushToStorage;
+}