Added sound effects throughout the app. Hear pieces move and capture, get audio feedback on check and checkmate, and enjoy sounds during puzzles and lessons. Sound effects can be toggled in Settings.

- Added sound effects for piece moves, captures, check, and checkmate
- Added sounds for game wins, losses, puzzle results, and lesson completion
- Added Sound Effects toggle in Settings under new Audio section
- Fixed deprecated API usage in Game Center integration
- Fixed empty location usage description