📦 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/utils/removeIgnoredSearchParams.js

@@ -0,0 +1,30 @@
+/*
+  Copyright 2018 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 '../_version.js';
+/**
+ * Removes any URL search parameters that should be ignored.
+ *
+ * @param {URL} urlObject The original URL.
+ * @param {Array<RegExp>} ignoreURLParametersMatching RegExps to test against
+ * each search parameter name. Matches mean that the search parameter should be
+ * ignored.
+ * @return {URL} The URL with any ignored search parameters removed.
+ *
+ * @private
+ * @memberof workbox-precaching
+ */
+export function removeIgnoredSearchParams(urlObject, ignoreURLParametersMatching = []) {
+    // Convert the iterable into an array at the start of the loop to make sure
+    // deletion doesn't mess up iteration.
+    for (const paramName of [...urlObject.searchParams.keys()]) {
+        if (ignoreURLParametersMatching.some((regExp) => regExp.test(paramName))) {
+            urlObject.searchParams.delete(paramName);
+        }
+    }
+    return urlObject;
+}