- Add clean texture variants (`piece_clean_N`) for merged pieces to remove outlines after grouping
- Improve piece renderer progress tracking to distinguish main vs. clean textures
- Support 140-piece puzzles (14×10 grid) across generator, menu, and selection scenes
- Auto-open join dialog when `?room=` URL parameter present in main menu
- Add shareable room link with copy-to-clipboard button in puzzle scene UI
- Introduce `_updatePieceEffects()` to manage visual states: clean textures for merged groups, drop shadows for singletons/groups
- Enhance music playback with fallback completion detection and robust event handling
Brian Fertig