📦 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/import-local/readme.md

@@ -0,0 +1,25 @@
+# import-local
+
+> Let a globally installed package use a locally installed version of itself if available
+
+Useful for CLI tools that want to defer to the user's locally installed version when available, but still work if it's not installed locally. For example, [AVA](https://avajs.dev) and [XO](https://github.com/xojs/xo) uses this method.
+
+## Install
+
+```sh
+npm install import-local
+```
+
+## Usage
+
+```js
+import importLocal from 'import-local';
+
+if (importLocal(import.meta.url)) {
+	console.log('Using local version of this package');
+} else {
+	// Code for both global and local version here…
+}
+```
+
+You can also pass in `__filename` when used in a CommonJS context.