- Add loading overlay (black background + "Loading..." text) behind UI panels
- Overlay starts visible by default, hidden in NativeConstruct if no sublevel
- CameraFade to black before sublevel load, with deferred fallback for BeginPlay
- 2s delay after OnLevelShown before starting 2s fade-in from black
- ShowLoadingScreen helper on PlayerController via HUD->MainWidget
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>