- Add engagement mode as new group activation option (mention | always | engagement)
- Probabilistic response when lurking (baseChance + triggerBoost for keywords)
- Always respond when engaged (100%) until cooldown
- Debounce message bursts (2.5s settle, 10s max) for coherent context
- Direct summons (trigger words, @mentions) bypass maxRatio limit
- Cooldown to lurking after silence (time or message count threshold)
- Preserve history across responses in engagement mode
- Fix @mention state tracking (was incorrectly marking as bot message)
