📦 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/detect-node/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "detect-node",
+  "version": "2.1.0",
+  "description": "Detect Node.JS (as opposite to browser environment) (reliable)",
+  "main": "index.js",
+  "module": "index.esm.js",
+  "browser": "browser.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/iliakan/detect-node"
+  },
+  "keywords": [
+    "detect",
+    "node"
+  ],
+  "author": "Ilya Kantor",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/iliakan/detect-node/issues"
+  },
+  "homepage": "https://github.com/iliakan/detect-node"
+}