feat(cluster): a SOTA column, and a spot click that credits the summit

The SOTA feeds put the summit in the spot's own text, so there is nothing to
poll: a regex on the comment gives the reference, and clicking the spot writes
SOTA@<ref> into the award references the way a park already wrote POTA@<ref>.

The regex is narrow on purpose — association/region-NNN, anchored — because
POTA (US-4475), WWFF (DLFF-0001) and portable callsigns (DL/SP9DPM/P) share
that field and none of them is a summit. Pinned by a table test.

Off by default: the reference is only there on the summit feeds, and an empty
column for every operator who does not chase them is worse than a checkbox.

frontend/src/components/ClusterGrid.tsx

@@ -45,6 +45,7 @@ export type ClusterSpot = {
   raw: string;
   repeats?: number;
   pota_ref?: string;
+  sota_ref?: string;
   pota_name?: string;
 };
 
@@ -336,6 +337,16 @@ const makeColCatalog = (t: TFn): ColEntry[] => [
       : { color: 'var(--success)' }) as any,
     tooltipValueGetter: (p: any) => (p.data?.pota_name ? t('clg2.tipPota', { name: p.data.pota_name }) : undefined),
   },
+  {
+    // SOTA sits next to POTA and reads the same way. The reference comes from the
+    // spot's comment, so it is present on the SOTA feeds and empty elsewhere —
+    // 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',
+    defaultVisible: false,
+    cellStyle: () => ({ color: 'var(--success)' }) as any,
+  },
   {
     group: 'Spot', label: t('clg2.c.freq'), colId: 'freq',
     headerName: t('clg2.c.freq'), field: 'freq_khz' as any, width: 95, type: 'rightAligned', cellClass: 'font-mono',