Add Hebat Allah wreck to the sunlit shallows site

First wreck in the production world layer. A WreckActor (StaticBody3D)
instantiates a two-LOD glTF visual, builds a trimesh collision from a
separate lighter glTF, and carries the sonar metadata (metal, 0.9
reflectivity) so the bathymetry rays echo it. The sunlit shallows site
places the MV Hebat Allah 62 m ahead of the submarine on the floor.

The assets derive from a CC BY 4.0 photogrammetry scan by Holger Buss
(Sketchfab). The raw 274 MB scan stays outside the repo; the committed
GLBs come from a reproducible Blender pipeline under scripts/assets/:
skirt cut, 44 m rescale, merge by distance (the scan is a triangle soup),
fragment removal, 0.4 m voxel remesh, decimation to 58k/14.5k/2.9k
triangles, smart UVs and a 2K albedo rebaked from a luminance-rebuilt
texture (the scan's red channel is dead).

docs/ASSET_LICENSES.md starts the licence registry required by the design
plan and records the attribution owed in the credits. The site suite
gains twelve assertions covering sonar metadata, collision, LOD handover
and triangle budgets. Godot extracts the embedded albedo next to the glb
on import; those PNGs are ignored like the cockpit ones.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/integration/run_sunlit_shallows_environment.gd

@@ -38,6 +38,7 @@ func _run() -> void:
 	_test_scattering_environment(site)
 	_test_air_fog_cut(site)
 	_test_surface_ceiling(site)
+	_test_wreck(site)
 
 	site.queue_free()
 	await process_frame
@@ -231,6 +232,70 @@ func _test_air_fog_cut(site: SunlitShallowsEnvironment) -> void:
 	)
 
 
+func _test_wreck(site: SunlitShallowsEnvironment) -> void:
+	var wreck := site.get_node_or_null("HebatAllahWreck") as WreckActor
+	_expect(wreck != null, "site places the Hebat Allah wreck")
+	if wreck == null:
+		return
+	_expect(
+		int(wreck.get_meta("sonar_material", SonarMaterial.Value.UNKNOWN))
+		== SonarMaterial.Value.METAL,
+		"wreck echoes as metal on the sonar"
+	)
+	_expect((wreck.collision_layer & 1) == 1, "wreck sits on the sonar collision layer")
+	_expect(
+		wreck.position.y < SunlitShallowsEnvironment.SURFACE_LEVEL_M
+		and absf(wreck.position.y - SunlitShallowsEnvironment.FLOOR_DEPTH_M) < 3.0,
+		"wreck rests on the site floor"
+	)
+	var collision := wreck.get_node_or_null(WreckActor.COLLISION_SHAPE_NAME) as CollisionShape3D
+	_expect(
+		collision != null and collision.shape is ConcavePolygonShape3D,
+		"wreck has a trimesh collision separate from its visuals"
+	)
+	if collision != null and collision.shape is ConcavePolygonShape3D:
+		var faces := (collision.shape as ConcavePolygonShape3D).get_faces()
+		_expect(faces.size() >= 3 * 500, "wreck collision mesh is not empty")
+		_expect(faces.size() <= 3 * 6000, "wreck collision mesh stays light")
+	var lod0 := wreck.find_child(WreckActor.LOD0_NODE_NAME, true, false) as MeshInstance3D
+	var lod1 := wreck.find_child(WreckActor.LOD1_NODE_NAME, true, false) as MeshInstance3D
+	_expect(lod0 != null and lod1 != null, "wreck carries two visual LODs")
+	if lod0 == null or lod1 == null:
+		return
+	_expect(
+		lod0.visibility_range_end > 0.0
+		and is_equal_approx(lod1.visibility_range_begin, lod0.visibility_range_end),
+		"wreck LODs hand over at one distance"
+	)
+	var lod0_triangles := _triangle_count(lod0.mesh)
+	var lod1_triangles := _triangle_count(lod1.mesh)
+	_expect(
+		lod0_triangles > 0 and lod0_triangles <= 120000,
+		"wreck LOD0 stays within the triangle budget"
+	)
+	_expect(lod1_triangles > 0 and lod1_triangles < lod0_triangles / 2, "wreck LOD1 is far lighter")
+	_expect(
+		lod0.mesh.surface_get_material(0) != null
+		or lod0.get_surface_override_material(0) != null,
+		"wreck LOD0 carries a material"
+	)
+
+
+func _triangle_count(mesh: Mesh) -> int:
+	if mesh == null:
+		return 0
+	var triangles := 0
+	for surface in mesh.get_surface_count():
+		var arrays := mesh.surface_get_arrays(surface)
+		var indices: PackedInt32Array = arrays[Mesh.ARRAY_INDEX]
+		if indices.is_empty():
+			var vertices: PackedVector3Array = arrays[Mesh.ARRAY_VERTEX]
+			triangles += vertices.size() / 3
+		else:
+			triangles += indices.size() / 3
+	return triangles
+
+
 func _expect(condition: bool, label: String) -> void:
 	_checks += 1
 	if not condition: