📦 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/core-js-compat/package.json

@@ -0,0 +1,31 @@
+{
+  "name": "core-js-compat",
+  "version": "3.49.0",
+  "type": "commonjs",
+  "description": "core-js compat",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/zloirock/core-js.git",
+    "directory": "packages/core-js-compat"
+  },
+  "homepage": "https://core-js.io",
+  "bugs": {
+    "url": "https://github.com/zloirock/core-js/issues"
+  },
+  "funding": {
+    "type": "opencollective",
+    "url": "https://opencollective.com/core-js"
+  },
+  "license": "MIT",
+  "author": {
+    "name": "Denis Pushkarev",
+    "email": "zloirock@zloirock.ru",
+    "url": "http://zloirock.ru"
+  },
+  "sideEffects": false,
+  "main": "index.js",
+  "types": "index.d.ts",
+  "dependencies": {
+    "browserslist": "^4.28.1"
+  }
+}