Add RoomSecret (5% chance) and RoomMiniBoss room types. Add 4 mini-boss monsters at 60% of boss stats (Guardian's Herald, Warden's Shadow, Overlord's Lieutenant, Archlich's Harbinger) with IsMiniBoss flag and boss pattern logic. Secret rooms grant double treasure. Mini-boss rooms are placed on floors 4/9/14/19 at room index 1. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>