Close the paint HUD when shutting down to player-less Main

ReleaseToNoPlayer tore down the mode cycle but never raised ModeChanged,
so the paint HUD - which only hides via that event - stayed open after a
shutdown that happened while PaintMode was active. Invoke ModeChanged(null)
after the teardown so any mode-following UI hides.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Scripts/GameModeManager.cs

@@ -223,6 +223,11 @@ public class GameModeManager : MonoBehaviour
         painter = null;
         PainterChanged?.Invoke(null);
 
+        // No SwitchTo runs here (the cycle is now empty), so notify mode-following UI explicitly that
+        // there is no active mode - otherwise the paint HUD, which only hides via ModeChanged, would stay
+        // open back in Main after a shutdown that happened while PaintMode was active.
+        ModeChanged?.Invoke(null);
+
         if (cameraInput)
             cameraInput.LookMode = ThirdPersonOrbitInput.OrbitLookMode.Disabled;