📦 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-recipes/staticResourceCache.js

@@ -0,0 +1,44 @@
+/*
+  Copyright 2020 Google LLC
+
+  Use of this source code is governed by an MIT-style
+  license that can be found in the LICENSE file or at
+  https://opensource.org/licenses/MIT.
+*/
+import { warmStrategyCache } from './warmStrategyCache';
+import { registerRoute } from 'workbox-routing/registerRoute.js';
+import { StaleWhileRevalidate } from 'workbox-strategies/StaleWhileRevalidate.js';
+import { CacheableResponsePlugin } from 'workbox-cacheable-response/CacheableResponsePlugin.js';
+import './_version.js';
+/**
+ * An implementation of the [CSS and JavaScript files recipe]{@link https://developers.google.com/web/tools/workbox/guides/common-recipes#cache_css_and_javascript_files}
+ *
+ * @memberof workbox-recipes
+ *
+ * @param {Object} [options]
+ * @param {string} [options.cacheName] Name for cache. Defaults to static-resources
+ * @param {RouteMatchCallback} [options.matchCallback] Workbox callback function to call to match to. Defaults to request.destination === 'style' || request.destination === 'script' || request.destination === 'worker';
+ * @param {WorkboxPlugin[]} [options.plugins] Additional plugins to use for this recipe
+ * @param {string[]} [options.warmCache] Paths to call to use to warm this cache
+ */
+function staticResourceCache(options = {}) {
+    const defaultMatchCallback = ({ request }) => request.destination === 'style' ||
+        request.destination === 'script' ||
+        request.destination === 'worker';
+    const cacheName = options.cacheName || 'static-resources';
+    const matchCallback = options.matchCallback || defaultMatchCallback;
+    const plugins = options.plugins || [];
+    plugins.push(new CacheableResponsePlugin({
+        statuses: [0, 200],
+    }));
+    const strategy = new StaleWhileRevalidate({
+        cacheName,
+        plugins,
+    });
+    registerRoute(matchCallback, strategy);
+    // Warms the cache
+    if (options.warmCache) {
+        warmStrategyCache({ urls: options.warmCache, strategy });
+    }
+}
+export { staticResourceCache };