fix(wb): latest lookup wins the worked-before panel

Two lookups race when a second callsign is typed before the first answered,
and the slow one landed last: the grid showed the previous call's QSOs under
the new call's name — LU5AVM's contact filed under LW8ETV, screenshot in
hand. A request token now discards any response that is not the newest.

frontend/src/App.tsx

@@ -4615,10 +4615,17 @@ export default function App() {
     return () => { dead = true; };
   }, [selQso, callsign]);
 
+  const wbTokenRef = useRef(0);
   async function runWorkedBefore(call: string, dxccHint: number = 0) {
+    // Latest-wins: two lookups race when the operator types a second call
+    // before the first answered, and the SLOW one used to land last — the
+    // grid then showed the previous call's QSOs under the new call's name
+    // (LU5AVM's contact filed under LW8ETV, screenshot in hand).
+    const token = ++wbTokenRef.current;
     setWbBusy(true);
     try {
       const w = await WorkedBefore(call, dxccHint);
+      if (token !== wbTokenRef.current) return; // a newer lookup owns the panel
       setWb(w);
       // Mirrored synchronously rather than through the effect above: a backfill
       // parked by the lookup has to read this on the very next line, not a
@@ -4633,10 +4640,11 @@ export default function App() {
         fillFromLastQso(p.r, call);
       }
     } catch {
+      if (token !== wbTokenRef.current) return;
       setWb(null);
       wbRef.current = null;
       wbCallRef.current = '';
-    } finally { setWbBusy(false); }
+    } finally { if (token === wbTokenRef.current) setWbBusy(false); }
   }
   // fillFromLastQso enriches the entry from the LAST QSO we logged with this call
   // when the live lookup came up short — the callsign isn't on QRZ/HamQTH, or no