feat(cluster): chase switches for POTA and SOTA

An operator who does not chase parks does not want NEW POTA shouting from every
activator spot. Two switches (Settings → DX Cluster, on by default): off, the
marker is withdrawn at the display layer — applySpotDisplay, the same chokepoint
the grid, the band map and the filter read through — so the badge, the colour,
the filter chip and the reference column all go quiet together, and a new-band +
new-POTA spot reads NEW BAND alone. The facts keep being computed; only the
telling stops, so ticking the box back on needs no rescan.

frontend/src/components/ClusterGrid.tsx

@@ -13,7 +13,7 @@ import { Button } from '@/components/ui/button';
 import { Checkbox } from '@/components/ui/checkbox';
 import { cleanSpotter, inferSpotMode, spotStatusKey } from '@/lib/spot';
 import { markerColour } from '@/lib/spotMarkers';
-import { applySpotDisplay, readSpotDisplayOptions } from '@/lib/spotDisplay';
+import { applySpotDisplay, chasePota, chaseSota, readSpotDisplayOptions } from '@/lib/spotDisplay';
 import { loadLocal, loadRemote, saveState, seedLocal, whenGridPrefsReady } from '@/lib/gridPrefs';
 import { distanceUnit, distanceValue, subscribeDistanceUnit } from '@/lib/units';
 import { useI18n } from '@/lib/i18n';
@@ -343,7 +343,9 @@ const makeColCatalog = (t: TFn): ColEntry[] => [
   },
   {
     group: 'Spot', label: t('clg2.c.pota'), colId: 'pota',
-    headerName: t('clg2.c.pota'), field: 'pota_ref' as any, width: 92, cellClass: 'font-mono',
+    headerName: t('clg2.c.pota'), width: 92, cellClass: 'font-mono',
+    // Through a valueGetter so the chase switch empties the column live.
+    valueGetter: (p: any) => (chasePota() ? p.data?.pota_ref ?? '' : ''),
     defaultVisible: true,
     cellStyle: (p: any) => (statusFor(p)?.new_pota
       ? fillStyle(markerColour('new_pota'))
@@ -356,7 +358,8 @@ const makeColCatalog = (t: TFn): ColEntry[] => [
     // which is why the column is off by default rather than an empty column for
     // everyone who does not watch summits.
     group: 'Spot', label: t('clg2.c.sota'), colId: 'sota',
-    headerName: t('clg2.c.sota'), field: 'sota_ref' as any, width: 100, cellClass: 'font-mono',
+    headerName: t('clg2.c.sota'), width: 100, cellClass: 'font-mono',
+    valueGetter: (p: any) => (chaseSota() ? p.data?.sota_ref ?? '' : ''),
     defaultVisible: false,
     cellStyle: () => ({ color: 'var(--success)' }) as any,
   },