feat: re-check for updates when opening Help - About (no more stale 'up to date')

Opening About now fires a fresh CheckForUpdate with a 'Checking…' state, and
clears the update banner when the latest check finds nothing — so it reflects
reality instead of the last periodic check.

frontend/src/App.tsx

@@ -1155,6 +1155,15 @@ export default function App() {
   }, []);
   const [showDuplicates, setShowDuplicates] = useState(false);
   const [updateInfo, setUpdateInfo] = useState<{ latest: string; url: string; downloadUrl: string } | null>(null);
+  const [checkingUpdate, setCheckingUpdate] = useState(false);
+  // Fresh update check on demand (opening About), so it never shows a stale
+  // "you're up to date". Clears updateInfo when the latest check finds nothing.
+  const checkUpdateNow = useCallback(() => {
+    setCheckingUpdate(true);
+    CheckForUpdate().then((u: any) => {
+      setUpdateInfo(u?.available && u?.latest ? { latest: String(u.latest), url: String(u.url ?? ''), downloadUrl: String(u.download_url ?? '') } : null);
+    }).catch(() => {}).finally(() => setCheckingUpdate(false));
+  }, []);
   const [updating, setUpdating] = useState(false);
   const [updateProgress, setUpdateProgress] = useState(0);
   const [updateError, setUpdateError] = useState('');
@@ -2831,7 +2840,7 @@ export default function App() {
       case 'tools.duplicates':  setShowDuplicates(true); break;
       case 'tools.refreshCty':  refreshCtyDat(); break;
       case 'tools.downloadRefs': downloadRefs(); break;
-      case 'help.about':        setShowAbout(true); break;
+      case 'help.about':        setShowAbout(true); checkUpdateNow(); break;
       case 'help.whatsnew':     GetChangelog().then((e: any) => { if (Array.isArray(e) && e.length) setWhatsNew(e); else showToast(t('whatsnew.none')); }).catch(() => {}); break;
     }
   }
@@ -4122,12 +4131,14 @@ export default function App() {
             </div>
             <p className="text-sm text-muted-foreground">Ham-radio logbook</p>
             <p className="mt-3 font-mono text-sm">version <span className="font-semibold text-foreground">{APP_VERSION}</span></p>
-            {updateInfo ? (
+            {checkingUpdate ? (
+              <p className="mt-1 text-[11px] text-muted-foreground inline-flex items-center gap-1"><Loader2 className="size-3 animate-spin" /> {t('upd.checking')}</p>
+            ) : updateInfo ? (
               <button onClick={() => updateInfo.url && BrowserOpenURL(updateInfo.url)} className="mt-1 text-xs text-primary underline hover:opacity-80">
                 Update available: v{updateInfo.latest} — download
               </button>
             ) : (
-              <p className="mt-1 text-[11px] text-success">You're up to date</p>
+              <p className="mt-1 text-[11px] text-success">{t('upd.upToDate')}</p>
             )}
             <p className="mt-3 text-sm">
               Developed by <span className="font-semibold text-primary">{APP_AUTHOR}</span>