📦 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/cookie-signature/package.json

@@ -0,0 +1,18 @@
+{
+  "name": "cookie-signature",
+  "version": "1.0.7",
+  "description": "Sign and unsign cookies",
+  "keywords": ["cookie", "sign", "unsign"],
+  "author": "TJ Holowaychuk <tj@learnboost.com>",
+  "license": "MIT",
+  "repository": { "type": "git", "url": "https://github.com/visionmedia/node-cookie-signature.git"},
+  "dependencies": {},
+  "devDependencies": {
+    "mocha": "*",
+    "should": "*"
+  },
+  "scripts": {
+    "test": "mocha --require should --reporter spec"
+  },
+  "main": "index"
+}