- Created DatabaseService.php with full OOP database abstraction layer
- Methods: select(), selectOne(), insert(), update(), delete(), execute(), count(), exists()
- Transaction support: beginTransaction(), commit(), rollback()
- Error handling: getLastError(), getLastQuery() for debugging
- Type-safe parameter binding with prepared statements
- Updated connection.php to initialize $db service
- Available globally as $db variable after connection.php include
- Foundation for migrating from procedural $conn queries
