fix: make non-walkable red blocks (Tile 4) invisible in 3D arenas

scenes/main.gd

@@ -177,17 +177,17 @@ func _instantiate_3d_arena(scene_path: String):
 
 func _hide_ground_tiles():
 	# Make normal and auxiliary ground floors invisible 
-	# by shrinking their scale to 0. We EXCLUDE Item 4 (Wall) and 5 (Freeze)
-	# so they can still be seen above the 3D arena.
+	# by shrinking their scale to 0. We also hide 4 (non-walkable red block) 
+	# as 3D arenas provide their own visual boundaries. We EXCLUDE 5 (Freeze).
 	var em = $EnhancedGridMap
 	if em and em.mesh_library:
 		var ml = em.mesh_library.duplicate()
-		for id in [0, 6]:
+		for id in [0, 4, 6]:
 			# Scale to 0 to hide it without triggering invalid mesh errors
 			ml.set_item_mesh_transform(id, Transform3D().scaled(Vector3.ZERO))
 		
 		em.mesh_library = ml
-		print("[Main] Hide tiles 0, 6 via zero-scale transform.")
+		print("[Main] Hide tiles 0, 4, 6 via zero-scale transform.")
 
 func _setup_effect_elevation():
 	var em = get_node_or_null("EnhancedGridMap")