📦 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/core-js-pure/modules/esnext.map.includes.js

@@ -0,0 +1,15 @@
+'use strict';
+var $ = require('../internals/export');
+var sameValueZero = require('../internals/same-value-zero');
+var aMap = require('../internals/a-map');
+var iterate = require('../internals/map-iterate');
+
+// `Map.prototype.includes` method
+// https://github.com/tc39/proposal-collection-methods
+$({ target: 'Map', proto: true, real: true, forced: true }, {
+  includes: function includes(searchElement) {
+    return iterate(aMap(this), function (value) {
+      if (sameValueZero(value, searchElement)) return true;
+    }, true) === true;
+  }
+});