- store: boomKey counter + boom() action
- Countdown fires boom() once when it reaches 0 (timer expiry only)
- Boom component (portal to body) plays a fullscreen white flash + giant 💥
- rendered at RoomPage level, keyed by boomKey so it plays fully (independent
of the countdown unmounting on reveal) and replays each round
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
