Implement CPU-side Naive Surface Nets for smooth voxel surfaces (SmoothStone,
Snow) coexisting with blocky voxels (Grass, Dirt, Stone, Sand).
Key features:
- SmoothMesher with binary SDF, centroid vertex placement, per-axis boundary
clamping to align with blocky grid at smooth↔blocky transitions
- Cross-chunk connectivity: PAD=2 SDF grid, vertex range [-1, CHUNK_SIZE),
canonical edge ownership (no duplicate triangles, no z-fighting)
- Face normals oriented by edge axis+sign (robust with binary SDF, unlike
SDF gradient dot or centroid sampling approaches)
- Y-axis winding fix: sharing cells have different spatial arrangement,
requiring opposite winding from X and Z axes
- GPU mesher treats smooth neighbors as solid (no blocky faces toward smooth)
- Material blending: primary (smooth-only) + secondary (all counts) per vertex
- Dedicated shaders: voxelSmoothVS (vertex pulling t6) + voxelSmoothPS
(triplanar + lerp blending between two materials)
- Separate render pass with LoadOp::LOAD after voxels+topings
- New materials: SmoothStone (mat 6), blocky Stone (mat 3) and Dirt patches
added to world generation for boundary testing
