feat(cluster): LoTW badge and filter, spotter-continent filter

The L badge is a single letter, not a word: the call column is 120 px and holds
a callsign. It keeps the muted blue of a confirmation and never a status colour,
because whether a station uploads to LoTW says nothing about whether the spot is
worth chasing - those are different questions and must not share a palette.

The spotter's continent is not the DX's. It asks whether anyone near you is
hearing the band at all, which is why it earns its own control rather than
reusing the existing Continent column. The spotter callsign now travels with the
status query so the backend can resolve it against the one DXCC prefix table,
instead of a second continent rule appearing in the frontend.

Both AND with the status chips rather than joining their OR: "a new band, and
from Europe" is the question being asked. An unresolved spot is never dropped by
them - the status arrives a moment after the row, and filtering meanwhile made
the list flicker.

New counties only is the SAME state as the NEW COUNTY chip, reached a second
way, not a second filter. County chasing is a mode you switch into, and hunting
for one chip among eight is not how you switch into it.

frontend/src/components/ClusterGrid.tsx

@@ -64,6 +64,11 @@ export type SpotStatusEntry = {
   new_pota?: boolean;
   new_pfx?: boolean;
   pfx?: string;
+  // lotw: the DX uploads to LoTW, per ARRL user list. Inert until downloaded.
+  lotw?: boolean;
+  spotter_continent?: string;
+  grid?: string;
+  new_grid?: boolean;
 };
 
 type Props = {
@@ -220,7 +225,21 @@ const makeColCatalog = (t: TFn): ColEntry[] => [
     cellRenderer: (p: any) => {
       const s = statusFor(p);
       const color = s?.status === 'new' ? null : s?.worked_call ? WKD : null;
-      return <span style={{ color: color ?? undefined, fontWeight: 700 }}>{p.value ?? ''}</span>;
+      return (
+        <span style={{ color: color ?? undefined, fontWeight: 700 }}>
+          {p.value ?? ''}
+          {/* A single letter rather than a word: the column is 120 px and holds a
+              callsign. It stays the muted-blue of a confirmation, never a status
+              colour — whether a station uploads to LoTW says nothing about
+              whether the spot is worth chasing. */}
+          {s?.lotw ? (
+            <span title={t('clu.lotwBadge')} style={{
+              marginLeft: 4, padding: '0 3px', borderRadius: 3, fontSize: 9, verticalAlign: 'middle',
+              background: 'color-mix(in srgb, var(--info) 22%, transparent)', color: 'var(--info)',
+            }}>L</span>
+          ) : null}
+        </span>
+      );
     },
     tooltipValueGetter: (p: any) => {
       const s = statusFor(p);