📦 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/process-nextick-args/readme.md

@@ -0,0 +1,18 @@
+process-nextick-args
+=====
+
+[![Build Status](https://travis-ci.org/calvinmetcalf/process-nextick-args.svg?branch=master)](https://travis-ci.org/calvinmetcalf/process-nextick-args)
+
+```bash
+npm install --save process-nextick-args
+```
+
+Always be able to pass arguments to process.nextTick, no matter the platform
+
+```js
+var pna = require('process-nextick-args');
+
+pna.nextTick(function (a, b, c) {
+  console.log(a, b, c);
+}, 'step', 3,  'profit');
+```