📦 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-abstract/2025/TimeString.js

@@ -0,0 +1,26 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var $isNaN = require('math-intrinsics/isNaN');
+
+var HourFromTime = require('./HourFromTime');
+var MinFromTime = require('./MinFromTime');
+var SecFromTime = require('./SecFromTime');
+var ToZeroPaddedDecimalString = require('./ToZeroPaddedDecimalString');
+
+// https://262.ecma-international.org/13.0/#sec-timestring
+
+module.exports = function TimeString(tv) {
+	if (typeof tv !== 'number' || $isNaN(tv)) {
+		throw new $TypeError('Assertion failed: `tv` must be a non-NaN Number');
+	}
+
+	var hour = ToZeroPaddedDecimalString(HourFromTime(tv), 2); // step 1
+
+	var minute = ToZeroPaddedDecimalString(MinFromTime(tv), 2); // step 2
+
+	var second = ToZeroPaddedDecimalString(SecFromTime(tv), 2); // step 3
+
+	return hour + ':' + minute + ':' + second + ' GMT'; // step 4
+};