fix(world): wind terrain triangles clockwise so the seabed is a front face

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/integration/run_site_terrain_integration.gd

@@ -15,7 +15,7 @@ const ReferenceBathymetryAcquisition = preload(
 )
 const DIVE_SITE_SCENE = preload("res://game/world/sites/dive_site.tscn")
 
-const TEST_COUNT := 23
+const TEST_COUNT := 24
 
 var _failures: Array[String] = []
 
@@ -68,6 +68,16 @@ func _test_actor_matches_field() -> void:
 	await physics_frame
 
 	_expect(actor.tile_count() == 4, "80 cells per side split into 2 x 2 tiles of 64")
+	var first_tile := actor.get_node("Tiles").get_child(0) as MeshInstance3D
+	var arrays: Array = first_tile.mesh.surface_get_arrays(0)
+	var tile_vertices: PackedVector3Array = arrays[Mesh.ARRAY_VERTEX]
+	var tile_indices: PackedInt32Array = arrays[Mesh.ARRAY_INDEX]
+	var first_face := Plane(
+		tile_vertices[tile_indices[0]],
+		tile_vertices[tile_indices[1]],
+		tile_vertices[tile_indices[2]]
+	)
+	_expect(first_face.normal.y > 0.0, "tile triangles are wound clockwise from above (front face up)")
 	var space := actor.get_world_3d().direct_space_state
 	var worst_error := 0.0
 	for cell: Vector2i in [