- Implement per-character voice clip system (match, supermatch, win, lose) that
loads lazily per round and falls back gracefully when clips are missing
- Queue voices to play after arcade cues, with intelligent interruption handling
so only one line plays at a time
- Rename ensureRoundBackgrounds to ensureRoundAssets to handle both images and audio
- Reduce background music volume from 0.8 to 0.4
- Update character sprite sheet and document voice clip structure in sprites.md
