fix(qsl): cancel an in-flight confirmation download on close / new download

The LoTW/QRZ confirmation download ran on the app-lifetime context, so it
kept going after the QSL Manager was closed and a new download didn't stop the
previous one. A slow QRZ sync therefore bled its "flag cleared" log into a
freshly started LoTW download — the operator saw QRZ activity during a LoTW
run. Now each download gets a cancellable context: starting one cancels the
previous, closing the window cancels it (CancelConfirmations), and the parse
loops bail promptly on cancel. (A LoTW http 503 is separate — ARRL's server.)

frontend/src/components/QSLManagerModal.tsx

@@ -8,7 +8,7 @@ import {
   Select, SelectTrigger, SelectValue, SelectContent, SelectItem,
 } from '@/components/ui/select';
 import { cn } from '@/lib/utils';
-import { FindQSOsForUpload, UploadQSOsManual, DownloadConfirmations, SyncPOTAHunterLog, ListQSO, BulkUpdateQSL, UploadCallsign, GetSlotStats } from '../../wailsjs/go/main/App';
+import { FindQSOsForUpload, UploadQSOsManual, DownloadConfirmations, CancelConfirmations, SyncPOTAHunterLog, ListQSO, BulkUpdateQSL, UploadCallsign, GetSlotStats } from '../../wailsjs/go/main/App';
 import { Input } from '@/components/ui/input';
 import { RecentQSOsGrid } from '@/components/RecentQSOsGrid';
 import { EventsOn } from '../../wailsjs/runtime/runtime';
@@ -120,6 +120,10 @@ export function QSLManagerPanel({ onEditQSO }: { onEditQSO?: (id: number) => voi
     if (service === 'pota' || service === 'paper') { setUploadCall(''); return; }
     UploadCallsign(service).then((c) => setUploadCall(c || '')).catch(() => setUploadCall(''));
   }, [service]);
+  // Closing the QSL Manager (the tab's ×) unmounts this panel — cancel any download
+  // still running so a slow QRZ/LoTW sync doesn't keep going in the background and
+  // bleed its log into the next one.
+  useEffect(() => () => { CancelConfirmations().catch(() => {}); }, []);
   const [potaSyncing, setPotaSyncing] = useState(false);
   const [potaRes, setPotaRes] = useState<POTASync | null>(null);
   const [potaErr, setPotaErr] = useState('');

frontend/wailsjs/go/main/App.d.ts

@@ -97,6 +97,8 @@ export function CIVTraceEnabled():Promise<boolean>;
 
 export function CWDecoderRunning():Promise<boolean>;
 
+export function CancelConfirmations():Promise<void>;
+
 export function ChatAvailable():Promise<boolean>;
 
 export function CheckForUpdate():Promise<main.UpdateInfo>;

frontend/wailsjs/go/main/App.js

@@ -142,6 +142,10 @@ export function CWDecoderRunning() {
   return window['go']['main']['App']['CWDecoderRunning']();
 }
 
+export function CancelConfirmations() {
+  return window['go']['main']['App']['CancelConfirmations']();
+}
+
 export function ChatAvailable() {
   return window['go']['main']['App']['ChatAvailable']();
 }