Clean up leftover studio worlds in either world layout

Studio worlds live in the "iris" world folder, which on 26.x is inside
the level's dimensions folder rather than in the world container.

Model used: Claude Opus 5.5

core/src/main/java/com/volmit/iris/Iris.java

@@ -93,6 +93,7 @@ public class Iris extends VolmitPlugin implements Listener {
     public static ChunkTickets tickets;
     private static VolmitSender sender;
     private static Thread shutdownHook;
+    private static final String STUDIO_WORLDS_FOLDER = "iris";
 
     static {
         try {
@@ -437,7 +438,7 @@ public class Iris extends VolmitPlugin implements Listener {
         services = new KMap<>();
         Bindings.setupSentry();
         initialize("com.volmit.iris.core.service").forEach((i) -> services.put((Class<? extends IrisService>) i.getClass(), (IrisService) i));
-        IO.delete(new File("iris"));
+        IO.delete(WorldStorage.get().worldFolder(STUDIO_WORLDS_FOLDER));
         compat = IrisCompat.configured(getDataFile("compat.json"));
         adoptLegacyWorldData();
         ServerConfigurator.configure();