Add arm closing to witness cleanup:
- Add closePolecatArm(name, reason) method that:
- Looks up arm ID in handoff state
- Closes the arm issue with the given reason
- Clears arm ID from handoff state
- Call closePolecatArm() at end of cleanupPolecat()
This completes the arm lifecycle: created when polecat discovered,
closed when polecat cleaned up. The Christmas Ornament pattern now
tracks the full polecat lifecycle.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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