📦 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.stat/out/settings.d.ts

@@ -0,0 +1,16 @@
+import * as fs from './adapters/fs';
+export interface Options {
+    followSymbolicLink?: boolean;
+    fs?: Partial<fs.FileSystemAdapter>;
+    markSymbolicLink?: boolean;
+    throwErrorOnBrokenSymbolicLink?: boolean;
+}
+export default class Settings {
+    private readonly _options;
+    readonly followSymbolicLink: boolean;
+    readonly fs: fs.FileSystemAdapter;
+    readonly markSymbolicLink: boolean;
+    readonly throwErrorOnBrokenSymbolicLink: boolean;
+    constructor(_options?: Options);
+    private _getValue;
+}