📦 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/unpipe/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "unpipe",
+  "description": "Unpipe a stream from all destinations",
+  "version": "1.0.0",
+  "author": "Douglas Christopher Wilson <doug@somethingdoug.com>",
+  "license": "MIT",
+  "repository": "stream-utils/unpipe",
+  "devDependencies": {
+    "istanbul": "0.3.15",
+    "mocha": "2.2.5",
+    "readable-stream": "1.1.13"
+  },
+  "files": [
+    "HISTORY.md",
+    "LICENSE",
+    "README.md",
+    "index.js"
+  ],
+  "engines": {
+    "node": ">= 0.8"
+  },
+  "scripts": {
+    "test": "mocha --reporter spec --bail --check-leaks test/",
+    "test-cov": "istanbul cover node_modules/mocha/bin/_mocha -- --reporter dot --check-leaks test/",
+    "test-travis": "istanbul cover node_modules/mocha/bin/_mocha --report lcovonly -- --reporter spec --check-leaks test/"
+  }
+}