feat(cluster): self-spot on the master node while logging

Settings -> DX Cluster: a toggle and an interval. When it is on, logging a QSO
announces the station on the master cluster — the QSO's own station callsign as
the DX, on the frequency the contact was made on — so callers find the run
without waiting for someone else to spot it. The node fills the DE field from
the login, so the spotter is us too: a self-spot.

It fires on the FIRST QSO of a frequency and then at most once per interval.
Both halves matter: announcing every QSO would flood the node and get the
station filtered out, while a pure timer would stay silent for minutes after a
band change. A drift of up to 500 Hz still counts as the same run, so nudging
the VFO mid-pileup does not re-announce.

Five minutes is the floor, clamped in SaveSelfSpotSettings as well as in the
input: the limit protects the node from us, so it must not depend on the
frontend. The interval input keeps raw text and clamps on blur — clamping per
keystroke rewrote "10" to "5" as soon as the "1" landed.

Wired into both log paths (manual entry and UDP auto-log) on the async side, so
a cluster that is slow or down never holds up logging. A send failure restores
the previous throttle state, so the next QSO retries instead of sitting out an
interval that produced no spot.

frontend/src/components/SettingsModal.tsx

@@ -26,7 +26,7 @@ import {
   AudioStartMonitor, AudioStopMonitor, AudioMonitorActive,
   AudioStartTX, AudioStopTX, AudioTXActive,
   ListClusterServers, SaveClusterServer, DeleteClusterServer,
-  GetClusterAutoConnect, SetClusterAutoConnect,
+  GetClusterAutoConnect, SetClusterAutoConnect, GetSelfSpotSettings, SaveSelfSpotSettings,
   ConnectClusterServer, DisconnectClusterServer,
   ConnectAllClusters, DisconnectAllClusters, GetClusterStatus,
   GetBackupSettings, SaveBackupSettings, RunBackupNow, PickBackupFolder,
@@ -1524,19 +1524,28 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
 
   const [clusterServers, setClusterServers] = useState<ClusterServer[]>([]);
   const [clusterAutoConnect, setClusterAutoConnectState] = useState(false);
+  // Self-spot. SELF_SPOT_MIN_MIN mirrors the backend floor — the input clamps on
+  // blur, not per keystroke, or typing "10" would be rewritten to "5" the moment
+  // the "1" landed and the field would fight the operator.
+  const SELF_SPOT_MIN_MIN = 5;
+  const [selfSpot, setSelfSpot] = useState({ enabled: false, minutes: SELF_SPOT_MIN_MIN });
+  const [selfSpotText, setSelfSpotText] = useState(String(SELF_SPOT_MIN_MIN));
   const [clusterStatuses, setClusterStatuses] = useState<ClusterServerStatus[]>([]);
   const [editingServer, setEditingServer] = useState<ClusterServer | null>(null);
 
   async function reloadClusterServers() {
     try {
-      const [list, ac, st] = await Promise.all([
+      const [list, ac, st, ss] = await Promise.all([
         ListClusterServers(),
         GetClusterAutoConnect(),
         GetClusterStatus(),
+        GetSelfSpotSettings(),
       ]);
       setClusterServers((list ?? []) as ClusterServer[]);
       setClusterAutoConnectState(ac);
       setClusterStatuses((st ?? []) as ClusterServerStatus[]);
+      setSelfSpot(ss as any);
+      setSelfSpotText(String((ss as any).minutes ?? SELF_SPOT_MIN_MIN));
     } catch (e: any) { setErr(String(e?.message ?? e)); }
   }
 
@@ -1849,6 +1858,7 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
       await SaveQSLDefaults(qslDefaults as any);
       await SaveExternalServices(extSvc as any);
       await SetClusterAutoConnect(clusterAutoConnect);
+      await SaveSelfSpotSettings(selfSpot as any);
 
       setMsg('Settings saved.');
       onSaved();
@@ -4114,6 +4124,39 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
               onCheckedChange={(c) => { const v = !!c; setClusterWorkedSameSlot(v); writeUiPref('opslog.clusterWorkedSameSlot', v ? '1' : '0'); }} />
             <span>{t('clu.workedSameSlot')} <span className="text-xs text-muted-foreground">{t('clu.workedSameSlotHint')}</span></span>
           </label>
+
+          {/* Self-spot. The interval only shows once it's on — an interval for
+              something switched off is just a question the operator can't act on. */}
+          <div className="border-t border-border/60 pt-3 space-y-2">
+            <div className="flex items-center gap-3 flex-wrap">
+              <label className="flex items-center gap-2 text-sm cursor-pointer">
+                <Checkbox checked={selfSpot.enabled}
+                  onCheckedChange={(c) => setSelfSpot((s) => ({ ...s, enabled: !!c }))} />
+                {t('clu.selfSpot')}
+              </label>
+              {selfSpot.enabled && (
+                <div className="flex items-center gap-2 text-sm">
+                  <span className="text-muted-foreground">{t('clu.selfSpotEvery')}</span>
+                  <Input
+                    type="number"
+                    min={SELF_SPOT_MIN_MIN}
+                    max={240}
+                    className="w-20 h-8 font-mono text-xs"
+                    value={selfSpotText}
+                    onChange={(e) => setSelfSpotText(e.target.value)}
+                    onBlur={() => {
+                      const n = Math.floor(Number(selfSpotText));
+                      const v = Number.isFinite(n) && n > SELF_SPOT_MIN_MIN ? Math.min(n, 240) : SELF_SPOT_MIN_MIN;
+                      setSelfSpotText(String(v));
+                      setSelfSpot((s) => ({ ...s, minutes: v }));
+                    }}
+                  />
+                  <span className="text-muted-foreground">{t('clu.selfSpotMinutes')}</span>
+                </div>
+              )}
+            </div>
+            <p className="text-xs text-muted-foreground leading-relaxed">{t('clu.selfSpotHint')}</p>
+          </div>
         </div>
 
         {editingServer && (