Add debug center lines for fuel barrel group

- Draw red horizontal line at deck vertical center
- Draw red vertical line through barrel group center
- Helps visualize alignment and centering

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/scenes/ShipDeckScene.js

@@ -158,6 +158,15 @@ export default class ShipDeckScene extends Phaser.Scene {
             this.showMessage(`Fuel supply: ${barrelCount} barrels (${this.inventory.fuel} units). Needed for boiling down whale blubber.`);
         });
         this.fuelBarrels.push(interactiveZone);
+
+        // Debug: Draw center lines for fuel barrel group
+        const centerLines = this.add.graphics();
+        centerLines.lineStyle(2, 0xFF0000, 0.8);
+        // Horizontal center line
+        centerLines.lineBetween(zoneX - zoneWidth / 2, deckVerticalCenter, zoneX + zoneWidth / 2, deckVerticalCenter);
+        // Vertical center line
+        centerLines.lineBetween(zoneX, zoneY - zoneHeight / 2, zoneX, zoneY + zoneHeight / 2);
+        this.fuelBarrels.push(centerLines);
     }
 
     createOilBarrels() {