feat(downloads): reset the saved column layout

Wire the download header reset action to cancel active column motion, restore the default order immediately, persist it through the serialized settings path, and confirm the result in the UI.

src/renderer/App.tsx

@@ -4805,6 +4805,20 @@ export function App(): ReactElement {
   }), [actionBusy, columnOrder, downloadDisclosureRevision, downloadPackageSpeeds, downloadQueueTotalBytes, downloadRemaining, downloadsSortColumn, downloadsSortDescending, downloadsViewCore, editingName, editingPackageId, gridTemplate, liveDownloadSpeedBps, providerStats.length, scheduleCountdown, schedulePickerOpen, scheduleTimeInput, snapshot.canPause, snapshot.canStart, snapshot.canStop, snapshot.clipboardActive, snapshot.etaText, snapshot.reconnectSeconds, snapshot.session.items, snapshot.session.paused, snapshot.session.reconnectReason, snapshot.session.running, snapshot.settings.animatePackageDisclosure, snapshot.settings.scheduledStartEpochMs, snapshot.stats.totalDownloaded, snapshot.stats.totalPackages]);
 
   const downloadsActions: DownloadsViewActions = {
+    onResetColumnLayout: () => {
+      if (columnDragSettleTimerRef.current !== null) {
+        window.clearTimeout(columnDragSettleTimerRef.current);
+        columnDragSettleTimerRef.current = null;
+      }
+      cancelColumnDragAnimations();
+      if (columnDragSessionRef.current) {
+        clearDownloadColumnDrag(columnDragSessionRef.current);
+        columnDragSessionRef.current = null;
+      }
+      setColumnOrder(DEFAULT_COLUMN_ORDER);
+      persistColumnOrder(DEFAULT_COLUMN_ORDER);
+      showToast("Spaltenlayout zurückgesetzt", 1800);
+    },
     onDisplayModeChange: setDownloadDisplayMode,
     onFilterChange: setDownloadFilter,
     onProviderFilterChange: setDownloadProviderFilter,