Fixed chess with FIDE rules

[roor48]

Implemented a fully functional chess game in the fun games menu with comprehensive rule support including all standard FIDE chess rules and draw conditions.

Changes

• ✅ Check detection: Kings cannot move into attacked squares
• ✅ Forced check resolution: When in check, only moves that resolve check are legal
• ✅ Checkmate: Game ends when king is in check with no legal moves
• ✅ Stalemate: Game ends in draw when no legal moves exist without being in check

Special Moves

• ✅ Castling
• ✅ En Passant

Draw Conditions

• ✅ Fifty-move rule
• ✅ Threefold repetition

Attack Detection & Validation

• ✅ Skewer detection: Squares behind pieces on attack lines are also marked as attacked
• ✅ Pin detection: Pieces pinned to king cannot move (enforced via check validation)
• ✅ Move validation: All moves are validated to not leave king in check

[RoflikBEST]

Thank you for your request, we've been wanting to update chess for a long time, you helped us.