📦 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/2023/ToNumber.js

@@ -0,0 +1,26 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $TypeError = require('es-errors/type');
+var $Number = GetIntrinsic('%Number%');
+var isPrimitive = require('../helpers/isPrimitive');
+
+var ToPrimitive = require('./ToPrimitive');
+var StringToNumber = require('./StringToNumber');
+
+// https://262.ecma-international.org/13.0/#sec-tonumber
+
+module.exports = function ToNumber(argument) {
+	var value = isPrimitive(argument) ? argument : ToPrimitive(argument, $Number);
+	if (typeof value === 'symbol') {
+		throw new $TypeError('Cannot convert a Symbol value to a number');
+	}
+	if (typeof value === 'bigint') {
+		throw new $TypeError('Conversion from \'BigInt\' to \'number\' is not allowed.');
+	}
+	if (typeof value === 'string') {
+		return StringToNumber(value);
+	}
+	return +value;
+};