📦 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/Iterator.from/implementation.js

@@ -0,0 +1,32 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var GetIteratorFlattenable = require('es-abstract/2025/GetIteratorFlattenable');
+var OrdinaryHasInstance = require('es-abstract/2025/OrdinaryHasInstance');
+var OrdinaryObjectCreate = require('es-abstract/2025/OrdinaryObjectCreate');
+
+var $Iterator = require('../Iterator/polyfill')();
+var $WrapForValidIteratorPrototype = require('../WrapForValidIteratorPrototype');
+
+var SLOT = require('internal-slot');
+
+module.exports = function from(O) {
+	if (this instanceof from) {
+		throw new $TypeError('`Iterator.from` is not a constructor');
+	}
+
+	var iteratorRecord = GetIteratorFlattenable(O, 'ITERATE-STRING-PRIMITIVES'); // step 1
+
+	var hasInstance = OrdinaryHasInstance($Iterator, iteratorRecord['[[Iterator]]']); // step 2
+
+	if (hasInstance) { // step 3
+		return iteratorRecord['[[Iterator]]']; // step 3.a
+	}
+
+	var wrapper = OrdinaryObjectCreate($WrapForValidIteratorPrototype); // , ['[[Iterated]]']); // step 4
+
+	SLOT.set(wrapper, '[[Iterated]]', iteratorRecord); // step 5
+
+	return wrapper; // step 6
+};