- daemon.go: Add SIGUSR1 handler to process lifecycle requests immediately
- handoff.go: Signal daemon after sending lifecycle mail to deacon/
- mail.go: Show message IDs in hook output for direct reading
Previously, gt handoff would wait up to 5 min for daemon heartbeat poll.
Now lifecycle requests are processed within milliseconds.
Closes gt-zut3
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>