fix: domino double-tap places tile on right end when both ends valid

Previously, tapping a tile that could play on both ends would highlight
board endpoints and require a separate canvas tap. Now a second tap on
the same tile auto-places it on the right end, matching mobile UX
expectations.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

public/js/modules/domino/scenes/game.js

@@ -503,10 +503,7 @@ function handleTileSelect(el, tile) {
   if (!playEnd) return;
 
   if (state.selectedTile?.id === tile.id) {
-    if (playEnd === 'both') {
-      board.setActiveEndpoint('both');
-      return;
-    }
+    // Second tap on same tile → place it (right end default for 'both')
     executePlacement(el, tile, playEnd === 'left' ? 'left' : 'right');
     return;
   }