Add `gt deacon stale-hooks` command to find and unhook stale beads.
Problem: Beads can get stuck in 'hooked' status when agents die or
abandon work without properly unhooking.
Solution:
- New command scans for hooked beads older than threshold (default 1h)
- Checks if assignee agent is still alive (tmux session exists)
- Unhooks beads with dead agents (sets status back to 'open')
- Supports --dry-run to preview without making changes
Also adds "stale-hook-check" step to Deacon patrol formula.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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