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.)

app.go

@@ -622,6 +622,12 @@ type App struct {
 	dvkRecSlot     int    // slot currently being recorded (DVKStartRecord → DVKStopRecord)
 	dvkPttKeyed    bool   // we keyed PTT for a voice message; unkey when it ends
 	pttMu          sync.Mutex
+	// confDLMu/confDLCancel cancel the in-flight confirmation download (LoTW/QRZ)
+	// so closing the QSL Manager — or starting another download — stops the previous
+	// one instead of leaving it running against the app-lifetime context (which made
+	// a still-running QRZ sync bleed its log into a freshly started LoTW download).
+	confDLMu       sync.Mutex
+	confDLCancel   context.CancelFunc
 	udpLogMu       sync.Mutex             // serialises UDP auto-log so concurrent packets can't both pass the dedup check
 	adifMonMu      sync.Mutex             // guards the ADIF-monitor config (file list + per-file read offsets)
 	relayAutoMu    sync.Mutex             // serialises relay auto-control evaluation
@@ -10180,13 +10186,35 @@ func (a *App) DownloadConfirmations(service string, addNotFound bool, since stri
 	}
 	svc := extsvc.Service(service)
 	cfg := a.loadExternalServices()
-	go a.runDownloadConfirmations(svc, cfg, addNotFound, since)
+	// Cancel any download still running (a slow QRZ sync, say) before starting this
+	// one, so the two don't run at once and interleave their logs — and derive a
+	// cancellable context so closing the QSL Manager can stop it too.
+	a.confDLMu.Lock()
+	if a.confDLCancel != nil {
+		a.confDLCancel()
+	}
+	ctx, cancel := context.WithCancel(a.ctx)
+	a.confDLCancel = cancel
+	a.confDLMu.Unlock()
+	go a.runDownloadConfirmations(ctx, svc, cfg, addNotFound, since)
 	return nil
 }
 
-func (a *App) runDownloadConfirmations(svc extsvc.Service, cfg extsvc.ExternalServices, addNotFound bool, since string) {
+// CancelConfirmations stops the in-flight LoTW/QRZ download — the QSL Manager
+// calls it when the window closes, so work doesn't keep running in the background.
+func (a *App) CancelConfirmations() {
+	a.confDLMu.Lock()
+	if a.confDLCancel != nil {
+		a.confDLCancel()
+		a.confDLCancel = nil
+	}
+	a.confDLMu.Unlock()
+}
+
+func (a *App) runDownloadConfirmations(ctx context.Context, svc extsvc.Service, cfg extsvc.ExternalServices, addNotFound bool, since string) {
 	emit := func(line string) {
-		if a.ctx != nil {
+		// Don't keep logging into a closed/cancelled window.
+		if a.ctx != nil && ctx.Err() == nil {
 			wruntime.EventsEmit(a.ctx, "qslmgr:log", line)
 		}
 	}
@@ -10195,7 +10223,6 @@ func (a *App) runDownloadConfirmations(svc extsvc.Service, cfg extsvc.ExternalSe
 			wruntime.EventsEmit(a.ctx, "qslmgr:done", map[string]any{"uploaded": matched, "total": total})
 		}
 	}
-	ctx := a.ctx
 	matched, total, added := 0, 0, 0
 
 	// resolveSince turns the UI's request into a concrete date (or ""):
@@ -10247,6 +10274,9 @@ func (a *App) runDownloadConfirmations(svc extsvc.Service, cfg extsvc.ExternalSe
 		var items []ConfirmationItem
 		var unmatched []string
 		perr := adif.Parse(strings.NewReader(adifText), func(rec adif.Record) error {
+			if ctx.Err() != nil {
+				return ctx.Err() // window closed / superseded
+			}
 			q, ok := adif.RecordToQSO(rec)
 			if !ok {
 				return nil
@@ -10429,6 +10459,9 @@ func (a *App) runDownloadConfirmations(svc extsvc.Service, cfg extsvc.ExternalSe
 		// QRZ FETCH returns headerless ADIF (no <EOH>); prepend one so the
 		// parser treats the stream as records.
 		perr := adif.Parse(strings.NewReader("<EOH>\n"+adifText), func(rec adif.Record) error {
+			if ctx.Err() != nil {
+				return ctx.Err() // window closed / superseded — stop clearing flags
+			}
 			parsed++
 			for k := range rec {
 				allKeys[k] = true
@@ -10598,6 +10631,9 @@ func (a *App) runDownloadConfirmations(svc extsvc.Service, cfg extsvc.ExternalSe
 		var items []ConfirmationItem
 		var unmatched []string
 		perr := adif.Parse(strings.NewReader(adifText), func(rec adif.Record) error {
+			if ctx.Err() != nil {
+				return ctx.Err() // window closed / superseded
+			}
 			q, ok := adif.RecordToQSO(rec)
 			if !ok {
 				return nil