📦 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-refresh/package.json

@@ -0,0 +1,34 @@
+{
+  "name": "react-refresh",
+  "description": "React is a JavaScript library for building user interfaces.",
+  "keywords": [
+    "react"
+  ],
+  "version": "0.11.0",
+  "homepage": "https://reactjs.org/",
+  "bugs": "https://github.com/facebook/react/issues",
+  "license": "MIT",
+  "files": [
+    "LICENSE",
+    "README.md",
+    "babel.js",
+    "runtime.js",
+    "build-info.json",
+    "cjs/",
+    "umd/"
+  ],
+  "main": "runtime.js",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/facebook/react.git",
+    "directory": "packages/react"
+  },
+  "engines": {
+    "node": ">=0.10.0"
+  },
+  "devDependencies": {
+    "react-16-8": "npm:react@16.8.0",
+    "react-dom-16-8": "npm:react-dom@16.8.0",
+    "scheduler-0-13": "npm:scheduler@0.13.0"
+  }
+}