📦 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/StringToCodePoints.js

@@ -0,0 +1,22 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var CodePointAt = require('./CodePointAt');
+
+// https://262.ecma-international.org/12.0/#sec-stringtocodepoints
+
+module.exports = function StringToCodePoints(string) {
+	if (typeof string !== 'string') {
+		throw new $TypeError('Assertion failed: `string` must be a String');
+	}
+	var codePoints = [];
+	var size = string.length;
+	var position = 0;
+	while (position < size) {
+		var cp = CodePointAt(string, position);
+		codePoints[codePoints.length] = cp['[[CodePoint]]'];
+		position += cp['[[CodeUnitCount]]'];
+	}
+	return codePoints;
+};