📦 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-precaching/getCacheKeyForURL.d.ts

@@ -0,0 +1,22 @@
+import './_version.js';
+/**
+ * Takes in a URL, and returns the corresponding URL that could be used to
+ * lookup the entry in the precache.
+ *
+ * If a relative URL is provided, the location of the service worker file will
+ * be used as the base.
+ *
+ * For precached entries without revision information, the cache key will be the
+ * same as the original URL.
+ *
+ * For precached entries with revision information, the cache key will be the
+ * original URL with the addition of a query parameter used for keeping track of
+ * the revision info.
+ *
+ * @param {string} url The URL whose cache key to look up.
+ * @return {string} The cache key that corresponds to that URL.
+ *
+ * @memberof workbox-precaching
+ */
+declare function getCacheKeyForURL(url: string): string | undefined;
+export { getCacheKeyForURL };