📦 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/vary/HISTORY.md

@@ -0,0 +1,39 @@
+1.1.2 / 2017-09-23
+==================
+
+  * perf: improve header token parsing speed
+
+1.1.1 / 2017-03-20
+==================
+
+  * perf: hoist regular expression
+
+1.1.0 / 2015-09-29
+==================
+
+  * Only accept valid field names in the `field` argument
+    - Ensures the resulting string is a valid HTTP header value
+
+1.0.1 / 2015-07-08
+==================
+
+  * Fix setting empty header from empty `field`
+  * perf: enable strict mode
+  * perf: remove argument reassignments
+
+1.0.0 / 2014-08-10
+==================
+
+  * Accept valid `Vary` header string as `field`
+  * Add `vary.append` for low-level string manipulation
+  * Move to `jshttp` orgainzation
+
+0.1.0 / 2014-06-05
+==================
+
+  * Support array of fields to set
+
+0.0.0 / 2014-06-04
+==================
+
+  * Initial release