📦 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/any-promise/register-shim.js

@@ -0,0 +1,18 @@
+"use strict";
+module.exports = require('./loader')(window, loadImplementation)
+
+/**
+ * Browser specific loadImplementation.  Always uses `window.Promise`
+ *
+ * To register a custom implementation, must register with `Promise` option.
+ */
+function loadImplementation(){
+  if(typeof window.Promise === 'undefined'){
+    throw new Error("any-promise browser requires a polyfill or explicit registration"+
+      " e.g: require('any-promise/register/bluebird')")
+  }
+  return {
+    Promise: window.Promise,
+    implementation: 'window.Promise'
+  }
+}