feat(deacon): improve timing and add heartbeat command

Timing changes for more relaxed poke intervals:
- Daemon heartbeat: 60s → 5 minutes
- Backoff base: 60s → 5 minutes
- Backoff max: 10m → 30 minutes
- Fresh threshold: <2min → <5min
- Stale threshold: 2-5min → 5-15min
- Very stale threshold: >5min → >15min

New command:
- `gt deacon heartbeat [action]` - Touch heartbeat file easily

Template rewrite:
- Clearer wake/sleep model
- Documents wake sources (daemon poke, mail, timer callbacks)
- Simpler rounds with `gt deacon heartbeat` instead of bash echo
- Mentions plugins as optional maintenance tasks
- Explains timer callbacks pattern

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/daemon/daemon.go

@@ -219,7 +219,7 @@ func (d *Daemon) pokeDeacon() {
 	}
 
 	// Send heartbeat message via tmux
-	msg := "HEARTBEAT: check Mayor and Witnesses"
+	msg := "HEARTBEAT: run your rounds"
 	if err := d.tmux.SendKeys(DeaconSessionName, msg); err != nil {
 		d.logger.Printf("Error poking Deacon: %v", err)
 		return