ContextWindow: Use Task.Run to load data outside main thread

Elwig/Windows/ContextWindow.cs

@@ -40,8 +40,11 @@ namespace Elwig.Windows {
         }
 
         protected async void OnLoaded(object? sender, RoutedEventArgs? evt) {
+            Mouse.OverrideCursor = Cursors.AppStarting;
             using var ctx = new AppDbContext();
             await OnRenewContext(ctx);
+            await OnInit(ctx);
+            Mouse.OverrideCursor = null;
         }
 
         protected async Task EnsureContextRenewed() {
@@ -51,6 +54,8 @@ namespace Elwig.Windows {
             _renewPending = false;
         }
 
+        virtual protected async Task OnInit(AppDbContext ctx) { }
+
         abstract protected Task OnRenewContext(AppDbContext ctx);
     }
 }