📦 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/escape-string-regexp/index.js

@@ -0,0 +1,13 @@
+'use strict';
+
+module.exports = string => {
+	if (typeof string !== 'string') {
+		throw new TypeError('Expected a string');
+	}
+
+	// Escape characters with special meaning either inside or outside character sets.
+	// Use a simple backslash escape when it’s always valid, and a \unnnn escape when the simpler form would be disallowed by Unicode patterns’ stricter grammar.
+	return string
+		.replace(/[|\\{}()[\]^$+*?.]/g, '\\$&')
+		.replace(/-/g, '\\x2d');
+};