test(notification-outbox): cover Discard and query-failure paths on the Outbox page

src/ScadaLink.CentralUI/Components/Pages/Monitoring/NotificationOutbox.razor

@@ -299,6 +299,8 @@
 
     private async Task RefreshAll()
     {
+        // Race-free despite both tasks mutating component fields: Blazor Server runs
+        // every continuation on the circuit's single-threaded synchronization context.
         await Task.WhenAll(LoadKpis(), FetchPage());
     }