📦 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/src/imageCache.ts

@@ -0,0 +1,77 @@
+/*
+  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 {CacheFirst} from 'workbox-strategies/CacheFirst.js';
+import {CacheableResponsePlugin} from 'workbox-cacheable-response/CacheableResponsePlugin.js';
+import {ExpirationPlugin} from 'workbox-expiration/ExpirationPlugin.js';
+import {
+  RouteMatchCallback,
+  RouteMatchCallbackOptions,
+  WorkboxPlugin,
+} from 'workbox-core/types.js';
+
+import './_version.js';
+
+export interface ImageCacheOptions {
+  cacheName?: string;
+  matchCallback?: RouteMatchCallback;
+  maxAgeSeconds?: number;
+  maxEntries?: number;
+  plugins?: Array<WorkboxPlugin>;
+  warmCache?: Array<string>;
+}
+
+/**
+ * An implementation of the [image caching recipe]{@link https://developers.google.com/web/tools/workbox/guides/common-recipes#caching_images}
+ *
+ * @memberof workbox-recipes
+ *
+ * @param {Object} [options]
+ * @param {string} [options.cacheName] Name for cache. Defaults to images
+ * @param {RouteMatchCallback} [options.matchCallback] Workbox callback function to call to match to. Defaults to request.destination === 'image';
+ * @param {number} [options.maxAgeSeconds] Maximum age, in seconds, that font entries will be cached for. Defaults to 30 days
+ * @param {number} [options.maxEntries] Maximum number of images that will be cached. Defaults to 60
+ * @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 imageCache(options: ImageCacheOptions = {}): void {
+  const defaultMatchCallback = ({request}: RouteMatchCallbackOptions) =>
+    request.destination === 'image';
+
+  const cacheName = options.cacheName || 'images';
+  const matchCallback = options.matchCallback || defaultMatchCallback;
+  const maxAgeSeconds = options.maxAgeSeconds || 30 * 24 * 60 * 60;
+  const maxEntries = options.maxEntries || 60;
+  const plugins = options.plugins || [];
+  plugins.push(
+    new CacheableResponsePlugin({
+      statuses: [0, 200],
+    }),
+  );
+  plugins.push(
+    new ExpirationPlugin({
+      maxEntries,
+      maxAgeSeconds,
+    }),
+  );
+
+  const strategy = new CacheFirst({
+    cacheName,
+    plugins,
+  });
+
+  registerRoute(matchCallback, strategy);
+
+  // Warms the cache
+  if (options.warmCache) {
+    warmStrategyCache({urls: options.warmCache, strategy});
+  }
+}
+
+export {imageCache};