4a49c76cdc
- Added holdPiece and canHold state to TetrisGame class - Implemented hold() method to swap current piece with held piece - Added player-hold socket event on server - Added HOLD preview canvas showing held piece (grayed when unavailable) - Added C key keyboard shortcut and touch button for hold - Fixed canHold reset on piece spawn for proper swap functionality Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>