Render grass blades as tapered ribbons

[Wanderwichtl]

Summary

• replace flattened three-sided cone blades with narrow, double-sided tapered ribbons
• preserve deterministic variants, wind material, and collective instancing
• reduce meadow geometry from 60 to 20 triangles per tuft and remove broad pyramid-like silhouettes

Validation

• bun run check-types
• bun test (16 passing)
• verified in the Pascal editor with 600 public trees:grass nodes across five instancing variants