feat(cluster): feed the locator store from PSK Reporter, filtered at the broker

The store shipped without its main source. Locators came only from this
station's own WSJT-X decodes, which is what the whole MQTT discussion was
about.

PSK Reporter now feeds it through a new OnGrid callback, fired before any
geographic filtering: what the store wants is "which square is this callsign
in", and that is true whoever happened to hear the report.

The subscription filters on the RECEIVER's square, a level the v2 topic
exposes. Measured on the live feed: the four opening bands unfiltered are 83
messages a second, of which roughly one in a hundred survived the NearKm test
that already existed here — the rest was received, TLS-decrypted, JSON-parsed
and discarded. One ring of squares is 0.2 to 1.2 a second.

By square rather than by DXCC, which was the obvious alternative: one country
measured 1.2 messages a second (OH) against 72.5 (K) on a single band, because
a DXCC can be a continent. By square the same measurement is 0.2 to 1.2, so the
load follows distance — what the feed is actually about — and is the same for
every operator.

Grid chasing subscribes with the "+" band wildcard, so one subscription per
square covers every band instead of one per band per square.

The store gains a source column (decode | mqtt), migrated in place on an
existing file.

frontend/src/components/SettingsModal.tsx

@@ -52,7 +52,7 @@ import {
   GetADIFMonitor, SaveADIFMonitor, PickADIFMonitorFile,
   GetRelayAuto, SaveRelayAuto, GetStationDevices,
   GetAwardDefs, GetTrackedAwards, SaveTrackedAwards,
-  GetBandOpenSettings, SaveBandOpenSettings, GetPSKReporterStatus, GetChaseNewGrids, SetChaseNewGrids,
+  GetBandOpenSettings, SaveBandOpenSettings, GetPSKReporterStatus, GetChaseNewGrids, SetChaseNewGrids, GetGridCacheStatus,
 } from '../../wailsjs/go/main/App';
 import type { profile as profileModels } from '../../wailsjs/go/models';
 import type { LookupSettingsForm, StationSettingsForm, ListsSettingsForm, ModePresetForm } from '@/types';
@@ -1553,6 +1553,7 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
   // feed up or down — so the write has to go where those live.
   const [bandOpen, setBandOpen] = useState<any>({ enabled: false, bands: [], available: [] });
   const [chaseGrids, setChaseGrids] = useState(false);
+  const [gridStat, setGridStat] = useState<any>(null);
   const [pskrStatus, setPskrStatus] = useState<any>(null);
   const saveBandOpen = async (next: any) => {
     setBandOpen(next);
@@ -1567,6 +1568,7 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
     // distinguishes "connected" from "connected and receiving nothing".
     const t = window.setInterval(async () => {
       try { setPskrStatus(await GetPSKReporterStatus()); } catch { /* ignore */ }
+      try { setGridStat(await GetGridCacheStatus()); } catch { /* ignore */ }
     }, 3000);
     return () => window.clearInterval(t);
   }, []);
@@ -4238,6 +4240,12 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
                 onCheckedChange={(c) => { setChaseGrids(!!c); SetChaseNewGrids(!!c).catch(() => {}); }} />
               <span>{t('clu.chaseGrids')} <span className="text-xs text-muted-foreground">{t('clu.chaseGridsHint')}</span></span>
             </label>
+            {chaseGrids && (
+              <p className="pl-6 text-xs text-muted-foreground">
+                {t('clu.chaseGridsStat', { n: gridStat?.known ?? 0, p: gridStat?.pending ?? 0 })}
+                {pskrStatus?.running ? ` · ${t('bo.feedUp', { n: pskrStatus.received ?? 0 })}` : ''}
+              </p>
+            )}
           </div>
 
           {/* Band-opening watch. It lives HERE, with the cluster nodes, because