📦 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/workbox-broadcast-update/responsesAreSame.d.ts

@@ -0,0 +1,14 @@
+import './_version.js';
+/**
+ * Given two `Response's`, compares several header values to see if they are
+ * the same or not.
+ *
+ * @param {Response} firstResponse
+ * @param {Response} secondResponse
+ * @param {Array<string>} headersToCheck
+ * @return {boolean}
+ *
+ * @memberof workbox-broadcast-update
+ */
+declare const responsesAreSame: (firstResponse: Response, secondResponse: Response, headersToCheck: string[]) => boolean;
+export { responsesAreSame };