Upgrade Ground Zero terrain material

Docs/Terrain/GroundZeroNaturalEnvironmentPass.md

@@ -6,7 +6,9 @@ space.
 
 ## Scope
 
-- Terrain receives a warm coastal scrub ground material.
+- Terrain receives a procedural coastal scrub terrain material that blends
+  dry soil, scrub green, and sandy path color families with broad and fine
+  noise so Ground Zero does not read as flat tan placeholder ground.
 - Foliage patch instances keep the current prototype meshes but use distinct
   tree, shrub, and dry grass materials.
 - Wood, fiber, stone, and freshwater actors receive distinct first-pass
@@ -48,7 +50,10 @@ space.
 `Scripts/verify_ground_zero_natural_environment_pass.py` checks that the
 materials exist, the landscape uses the terrain material, the foliage actor has
 the expected investor-facing instance counts and material assignments, and
-resource/water actors are visually dressed. It also checks the asset variation
+resource/water actors are visually dressed. It also checks that the terrain
+material contains procedural color breakup rather than a flat constant color:
+noise, blend, and coastal-scrub color-vector expression families must be present
+in the saved material package. It also checks the asset variation
 layer: twenty-three labeled variation actors, at least four mesh silhouettes,
 unique scale profiles, and coverage across tree, bush, grass, rock, and water
 visual families. `Scripts/verify_native_placeholder_meshes.py` checks that playable