fix: cast Chessground check prop to fix build type error

GameNode.check is boolean but Chessground expects
boolean | 'white' | 'black' | undefined, causing a build
failure on Vercel with stricter type checking.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ashtonanderson

src/components/Board/GameBoard.tsx

@@ -170,7 +170,7 @@ export const GameBoard: React.FC<Props> = ({
           },
           fen: boardConfig.fen,
           lastMove: boardConfig.lastMove as Key[],
-          check: boardConfig.check,
+          check: boardConfig.check as boolean | 'white' | 'black' | undefined,
           orientation: boardConfig.orientation,
         }}
       />