Stone: add corner fill triangles at adjacent open edges and cap
triangles at strip terminaisons. Grass: replace bevel strips with
tuft-based grass blades — clusters of 3-9 curved double-sided
blades with per-tuft height/lean personality and hash-driven
placement (quadratic inset 0-0.30 from edge). Vegetation PS uses
half-Lambert wrap lighting + translucency for soft stylized shading
(inspired by Airborn Trees). Stone keeps classic Lambert.
Add instanced rendering for toping bevels: dedicated shaders
(voxelTopingVS/PS), PSO, GPU buffers (t4 vertices, t5 instances),
per-group DrawInstanced in a separate render pass with LoadOp::LOAD.
Fix inverted face winding (emitTri auto-winding condition flipped for
CW front-facing), slope normals (use inward direction not outward),
and PS lighting (negate sunDirection like voxelPS). Update CLAUDE.md
with Phase 4.1/4.2 documentation.
