Smoother world streaming and floor preview
New
- The minimap has up/down buttons to preview floors from -10 to +10 and displays the selected level. Movement preserves manual selection; recentering restores your character's floor.
Fixed
- Reduced stuttering when crossing chunk boundaries. Shadow creation, map effects and minimap copies no longer perform all their heavy work in one frame. Leaving a map also cleans up unfinished chunks.

