fix: correct overlay node path in MainGame signal handlers

MainGame.gd

@@ -75,10 +75,10 @@ func _unhandled_input(event: InputEvent) -> void:
 	$SceneViewport.push_input(event)
 	
 func _on_backpack_show_overlay() -> void:
-	$HUD/InventoryOverlay.show_overlay()
+	$InventoryOverlayLayer/InventoryOverlay.show_overlay()
 
 func _on_backpack_hide_overlay() -> void:
-	$HUD/InventoryOverlay.hide_overlay()
+	$InventoryOverlayLayer/InventoryOverlay.hide_overlay()
 
 func _input(event):
 	if event.is_action_released("quit"):