Add Ground Zero ruin landmark placeholder

Docs/Terrain/GroundZeroNaturalEnvironmentPass.md

@@ -14,6 +14,9 @@ space.
 - First-pass asset variation actors add additional tree canopies/trunks, rounded
   bushes, grass mats, rock slabs, and a visible freshwater surface with varied
   meshes, scales, rotations, and material families.
+- A first-pass ruin landmark placeholder gives the Ground Zero demo a visible
+  point of interest using five native placeholder stone pieces: foundation,
+  wall fragments, a cairn marker, and a threshold.
 - The foliage and asset variation layers now use Agrarian-native placeholder
   mesh assets from `/Game/Agrarian/Environment/PlaceholderMeshes` instead of
   direct `LevelPrototyping` mesh references.
@@ -49,7 +52,9 @@ profiles, and coverage across tree, bush, grass, rock, and water visual
 families. `Scripts/verify_native_placeholder_meshes.py` checks that playable
 resource/structure/water Blueprints, foliage components, and environment
 variation actors use Agrarian-native placeholder meshes rather than template
-mesh paths.
+mesh paths. `Scripts/verify_ground_zero_landmark_placeholder.py` checks the
+ruin landmark placeholder actor count, native mesh paths, stone material
+assignment, distinct placement, and roadmap/doc coverage.
 
 ## Follow-Up