- Add gear.png and pipe.png sprite assets for GooTower
- Replace procedural drawGears() with rotated sprite instances for better performance
- Replace procedural drawPipe() with sprite art and separate procedural glow overlay
- Add patchy grass strips along top-facing terrain edges with variable depth and two-tone coloring
- Add mottled dirt texture pass clipped to polygon bounds
- Introduce helper functions (hash01, topFacingEdges, pointInPoly) for texture rendering
- Update asset manifest to include new gootower images
