📦 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-window/messageSW.d.ts

@@ -0,0 +1,17 @@
+import './_version.js';
+/**
+ * Sends a data object to a service worker via `postMessage` and resolves with
+ * a response (if any).
+ *
+ * A response can be set in a message handler in the service worker by
+ * calling `event.ports[0].postMessage(...)`, which will resolve the promise
+ * returned by `messageSW()`. If no response is set, the promise will not
+ * resolve.
+ *
+ * @param {ServiceWorker} sw The service worker to send the message to.
+ * @param {Object} data An object to send to the service worker.
+ * @return {Promise<Object|undefined>}
+ * @memberof workbox-window
+ */
+declare function messageSW(sw: ServiceWorker, data: {}): Promise<any>;
+export { messageSW };