Implement RandomEvent system with 8 events (altar, fountain, merchant,
trap_room, shrine, chest, ghost, mushroom), each with 2-3 choices that
resolve based on floor number. Update triggerEvent() to use the new
system, auto-resolving a random choice on a random alive player.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
