Checkers (Draughts) Redesigned with Material 3 Expressive

The Checkers game has been redesigned with Material 3 Expressive design, featuring warm brown gradients (#8d6e63 → #a1887f) matching the classic board aesthetic, 28px rounded game board container with gradient squares, polished checker pieces with gradient fills and enhanced king styling, M3 toggle buttons for difficulty selection, gradient-styled stats chips, and improved status alerts.