fix: Stations-on-air widget lagged minutes (timer reset by dbConn object churn)

The 15s poll effect depended on the dbConn OBJECT, which gets a fresh reference
on several events — each reset the interval before it fired, so the widget could
stay stale for over a minute. Depend on the is-mysql boolean instead, and also
refresh ~2s after qso:logged so our own row appears promptly like the ON AIR
badge.

frontend/src/App.tsx

@@ -441,13 +441,21 @@ export default function App() {
   type LiveStation = { operator: string; station: string; freq_hz: number; band: string; mode: string; online: boolean; version: string; age_sec: number };
   const [liveStations, setLiveStations] = useState<LiveStation[]>([]);
   const [showLiveStations, setShowLiveStations] = useState(() => localStorage.getItem('opslog.showLiveStations') === '1');
+  // Depend on the BOOLEAN (is-mysql), not the dbConn object: dbConn gets a fresh
+  // reference on several events, and depending on the object reset the 15s timer
+  // on every such refresh so it could ~never fire (the widget looked stuck for
+  // minutes). Also refresh right after we log a QSO so our own row shows without
+  // waiting for the next tick, like the ON AIR badge.
+  const liveStationsOn = dbConn?.backend === 'mysql';
   useEffect(() => {
-    if (dbConn?.backend !== 'mysql') { setLiveStations([]); return; }
+    if (!liveStationsOn) { setLiveStations([]); return; }
     const load = () => GetLiveStations().then((s) => setLiveStations((s ?? []) as LiveStation[])).catch(() => {});
     load();
     const id = window.setInterval(load, 15 * 1000);
-    return () => window.clearInterval(id);
-  }, [dbConn]);
+    // Small delay lets the async publishLiveStatus MySQL write land before we read.
+    const offLogged = EventsOn('qso:logged', () => { window.setTimeout(load, 2000); });
+    return () => { window.clearInterval(id); offLogged?.(); };
+  }, [liveStationsOn]);
   // Mode OpsLog shows when the rig reports generic DIG_U/DIG_L. OmniRig
   // can't tell us if it's FT8 vs FT4 vs RTTY, so the user picks the default
   // in Preferences > Hardware > CAT interface.