Boss phases, skill AI, and combat fixes

Boss fights now have real phase transitions. Push a boss below its threshold and its behavior changes mid-fight — the Rootmother gets faster, Dregthar hits harder. Each boss has a unique transition with a combat log callout so you know when the fight just got serious.

Legendary cooldown reduction effects now work properly. The Hive Mind effect on Rootmother's Embrace actually reduces your skill cooldowns each turn as intended. At higher tiers, this meaningfully speeds up your skill rotation.

DoT stacking is now capped at 3 concurrent effects. Reapplying the same bleed or poison refreshes its duration instead of stacking copies. If you're already at the cap, the oldest effect gets replaced.

Skill AI is smarter about when to use abilities. Burst damage is prioritized when an enemy is close to death instead of wasting turns on buffs or DoTs that won't tick enough times to matter.