Rewrote voxelSmoothPS.hlsl to derive a dominant face axis from the smooth
normal, then use the exact same neighbor verification as voxelPS.hlsl:
faceU/faceV tangent tables, stair-priority getNeighborMat(), face-aligned
fractional coords, blendZone 0.25, corner attenuation, bleedMask checks.
Added generateDebugSmooth() with 11 isolated test configurations
(smooth↔blocky transitions, staircases, surrounded patches, reference
blocky pairs). Launch with: BVLEVoxels.exe debugsmooth