📦 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/chrome-trace-event/README.md

@@ -0,0 +1,31 @@
+[![Build Status](https://travis-ci.org/samccone/chrome-trace-event.svg?branch=master)](https://travis-ci.org/samccone/chrome-trace-event)
+
+chrome-trace-event: A node library for creating trace event logs of program
+execution according to [Google's Trace Event
+format](https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU).
+These logs can then be visualized with
+[trace-viewer](https://github.com/google/trace-viewer) or chrome devtools to grok one's programs.
+
+# Install
+
+    npm install chrome-trace-event
+
+# Usage
+
+```javascript
+const Trace = require("chrome-trace-event").Tracer;
+const trace = new Trace({
+    noStream: true
+});
+trace.pipe(fs.createWriteStream(outPath));
+trace.flush();
+```
+
+# Links
+
+* https://github.com/google/trace-viewer/wiki
+* https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU
+
+# License
+
+MIT. See LICENSE.txt.