📦 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/react/README.md

@@ -0,0 +1,37 @@
+# `react`
+
+React is a JavaScript library for creating user interfaces.
+
+The `react` package contains only the functionality necessary to define React components. It is typically used together with a React renderer like `react-dom` for the web, or `react-native` for the native environments.
+
+**Note:** by default, React will be in development mode. The development version includes extra warnings about common mistakes, whereas the production version includes extra performance optimizations and strips all error messages. Don't forget to use the [production build](https://reactjs.org/docs/optimizing-performance.html#use-the-production-build) when deploying your application.
+
+## Usage
+
+```js
+import { useState } from 'react';
+import { createRoot } from 'react-dom/client';
+
+function Counter() {
+  const [count, setCount] = useState(0);
+  return (
+    <>
+      <h1>{count}</h1>
+      <button onClick={() => setCount(count + 1)}>
+        Increment
+      </button>
+    </>
+  );
+}
+
+const root = createRoot(document.getElementById('root'));
+root.render(<App />);
+```
+
+## Documentation
+
+See https://reactjs.org/
+
+## API
+
+See https://reactjs.org/docs/react-api.html