feat: deselect card on empty space click in SkipBo

- Add pointerdown listener to clear selectedSource and highlights when clicking empty space.
- Improves UX by allowing players to easily cancel card selection.

public/src/games/skipbo/SkipBoGame.js

@@ -287,6 +287,16 @@ export default class SkipBoGame extends Phaser.Scene {
     new Button(this, 110, GAME_HEIGHT - 100, 'Leave', () => this.scene.start('GameMenu'), {
       variant: 'ghost', width: 110, height: 40, fontSize: 18,
     }).setDepth(D.ui);
+
+    // Clicking empty space deselects the current card
+    this.input.on('pointerdown', (pointer) => {
+      if (!this.selectedSource) return;
+      if (this.input.hitTestPointer(pointer).length === 0) {
+        this.selectedSource = null;
+        this.clearHighlights();
+        this.setStatus('Your turn');
+      }
+    });
   }
 
   // ── Game start ───────────────────────────────────────────────────────────