refactor: see details below

- Fix emailing.
- Updated manage.sh to enhance command handling and service management for backend and frontend.
- Introduced utility functions for better code organization and readability.
- Added support for checking Node.js version and ensuring the virtual environment is set up.
- Implemented improved logging with color-coded output for better visibility.
- Created a new nginx.conf.example file for easy Nginx configuration setup for the application.

.env.example

@@ -7,7 +7,7 @@
 # DATABASE_URL=postgresql://user:password@localhost/checkin
 
 # CORS 允许的前端域名（逗号分隔，生产环境必须修改）
-CORS_ORIGINS=http://localhost:5173,http://localhost:3000
+CORS_ORIGINS=http://localhost:3000
 
 # 日志级别（可选：DEBUG, INFO, WARNING, ERROR）
 LOG_LEVEL=INFO