📦 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/es-iterator-helpers/aos/IfAbruptCloseIterators.js

@@ -0,0 +1,19 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var CompletionRecord = require('es-abstract/2025/CompletionRecord');
+var IteratorCloseAll = require('./IteratorCloseAll');
+
+// https://tc39.es/proposal-joint-iteration/#sec-ifabruptcloseiterators
+
+module.exports = function IfAbruptCloseIterators(value, iteratorRecords) {
+	if (!(value instanceof CompletionRecord)) {
+		throw new $TypeError('Assertion failed: `value` must be a Completion Record'); // step 1
+	}
+	if (value.type() === 'throw') {
+		return IteratorCloseAll(iteratorRecords, value); // step 2
+	}
+
+	return value['!'](); // step
+};