Add deacon package with heartbeat read/write helpers:
- Heartbeat struct with Timestamp, Cycle, LastAction, health counts
- WriteHeartbeat/ReadHeartbeat for persistence to deacon/heartbeat.json
- IsFresh/IsStale/IsVeryStale for age checks
- ShouldPoke to determine if daemon should wake the Deacon
- Touch/TouchWithAction convenience functions
The Deacon writes heartbeat on each wake cycle. The Go daemon reads it
to decide whether to poke the Deacon (only if very stale >5 minutes).
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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