- Add new `wallArt` level data array with per-cell decal frames
- Integrate wall art rendering into WolfensteinView using same texture sampling as walls
- Add Wall Art tool to WolfensteinEditor with dynamic dropdown from JSON registry
- Create wolfenstein-wallart.json frame registry for easy decal management
- Add validation ensuring wall art sits on actual wall cells
- Support wall art in save/load system with backward compatibility
- Alert idle enemies when shot, even outside vision cone