feat(slack): implement thread ownership policy for multi-bot scenarios

[aaronwong1989]

Summary

In channels with multiple HotPlex bots, when a user creates a Thread, multiple bots responding simultaneously creates noise. Implement Thread Ownership Policy: first bot mentioned in a Thread owns that thread. owner responds to all messages, other bots stay silent unless explicitly @mentioned.

Design Doc

• Spec: bot-behavior-spec.md

Scope

Phase 1: MVP (Required) ✅ COMPLETE

• @mention detection and response
• Respond in thread (not channel message)
• Owner policy configuration
• Thread ownership tracking (bot-centric model)
• Ownership transfer on @mention (R3)
• Multi-owner support (independent bot tracking)
• TTL expiration

Phase 2: Enhanced UX

• Implicit trigger detection
• Silence commands
• Thread lifecycle (done/continue)
• DM behavior

Phase 3: Advanced

• Multi-bot coordination
• Proactive behavior

Core Rules (from Spec)

Context	@ Mention	No @
Main Channel	Mentioned bots respond (per policy)	All bots silent
Owned Thread	Owner + mentioned bots respond	Owner responds
Unowned Thread	Mentioned bots claim & respond	All bots silent

Config

bot:
  owner:
    primary: "U12345"
    trusted: []
    policy: owner_only  # owner_only | trusted | public

  thread_ownership:
    enabled: true
    ttl: 24h
    persist: true