📦 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/get-own-enumerable-property-symbols/README.md

@@ -0,0 +1,15 @@
+# get-own-enumerable-property-symbols [![Build Status](https://travis-ci.org/mightyiam/get-own-enumerable-property-symbols.svg?branch=master)](https://travis-ci.org/mightyiam/get-own-enumerable-property-symbols)
+
+Returns an array of all *enumerable* symbol properties found directly upon a given object.
+
+Similar to [`Object.getOwnPropertySymbols`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getOwnPropertySymbols)
+but only [enumerable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties) keys.
+
+```js
+import getOwnEnumPropSymbols from 'get-own-enumerable-property-symbols'
+
+getOwnEnumPropSymbols({ [Symbol()]: undefined })
+// [Symbol()]
+getOwnEnumPropSymbols(Object.defineProperty({}, Symbol(), {enumerable: false}))
+// []
+```