fix: who's-on-air freq/appearance lag — prompt publish on activity + 5s widget poll

publishLiveStatus only ran on QSO log or the 15s heartbeat, and the widget polled
every 15s, so an operator's band/freq (and their appearance) could trail by up to
a minute. Now ReportLiveActivity debounce-publishes ~1.5s after a freq/band/mode
change, and the widget polls every 5s (and 1.5s after qso:logged).

app.go

@@ -508,6 +508,7 @@ type App struct {
 	liveFreqHz         int64      // last freq/band/mode the UI reported (fallback when CAT is off)
 	liveBand           string
 	liveMode           string
+	livePublishTimer   *time.Timer // debounced live-status publish on activity change
 	liveLastQSOAt      time.Time  // when this operator last logged a NEW contact — drives online/offline
 	awardSnapMu        sync.Mutex // guards the award QSO snapshot
 	awardSnap          []qso.QSO  // light-scanned + enriched logbook snapshot reused across award computations