* feat: Add MySQL database support
- Add MySQL database support with environment-based configuration
- Fix MySQL compatibility issue with 'key' column name
- Maintain SQLite as default database
- Add proper validation for MySQL configuration
- Test and verify compatibility with existing database
- Replaced raw SQL queries using JSON_EACH functions with standard GORM queries
- Modified functions to handle JSON parsing in Go code instead of database since JSON_EACH is not available on MySQL or MariaDB:
- getAllEmails()
- GetClientTrafficByID()
- getFallbackMaster()
- MigrationRemoveOrphanedTraffics()
The system now supports both MySQL and SQLite databases, with SQLite remaining as the default option. MySQL connection is only used when explicitly configured through environment variables.
* refactor: prefix env variables of database with XUI_ to support direct environment usage without .env file
All database configuration environment variables now start with the XUI_ prefix to avoid conflicts and allow configuration via system-level environment variables, not just the .env file.
