📦 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.d.ts

@@ -0,0 +1,18 @@
+/**
+Escape RegExp special characters.
+
+You can also use this to escape a string that is inserted into the middle of a regex, for example, into a character class.
+
+@example
+```
+import escapeStringRegexp = require('escape-string-regexp');
+
+const escapedString = escapeStringRegexp('How much $ for a 🦄?');
+//=> 'How much \\$ for a 🦄\\?'
+
+new RegExp(escapedString);
+```
+*/
+declare const escapeStringRegexp: (string: string) => string;
+
+export = escapeStringRegexp;