📦 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/path-to-regexp/package.json

@@ -0,0 +1,30 @@
+{
+  "name": "path-to-regexp",
+  "description": "Express style path to RegExp utility",
+  "version": "0.1.13",
+  "files": [
+    "index.js",
+    "LICENSE"
+  ],
+  "scripts": {
+    "test": "istanbul cover _mocha -- -R spec"
+  },
+  "keywords": [
+    "express",
+    "regexp"
+  ],
+  "component": {
+    "scripts": {
+      "path-to-regexp": "index.js"
+    }
+  },
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/pillarjs/path-to-regexp.git"
+  },
+  "devDependencies": {
+    "mocha": "^1.17.1",
+    "istanbul": "^0.2.6"
+  }
+}