📦 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/merge-stream/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "merge-stream",
+  "version": "2.0.0",
+  "description": "Create a stream that emits events from multiple other streams",
+  "files": [
+    "index.js"
+  ],
+  "scripts": {
+    "test": "istanbul cover test.js && istanbul check-cover --statements 100 --branches 100"
+  },
+  "repository": "grncdr/merge-stream",
+  "author": "Stephen Sugden <me@stephensugden.com>",
+  "license": "MIT",
+  "dependencies": {},
+  "devDependencies": {
+    "from2": "^2.0.3",
+    "istanbul": "^0.4.5"
+  }
+}