Refactor theme change handler for safe async updates

Refactored OnThemeChanged in MainLayout.razor to use InvokeAsync for proper synchronization of UI updates and async logic, preventing threading issues. Also added a blank line after app.Run() in Program.cs (no functional impact).

DbFirst.BlazorWebApp/Components/Layout/MainLayout.razor

@@ -50,13 +50,14 @@
         await ApplyDxDarkOverrideAsync();
     }
 
-    private async void OnThemeChanged()
+    private void OnThemeChanged()
     {
-        StateHasChanged();
-        if (_isInteractive)
+        InvokeAsync(async () =>
         {
-            await ApplyDxDarkOverrideAsync();
-        }
+            StateHasChanged();
+            if (_isInteractive)
+             await ApplyDxDarkOverrideAsync();
+        });
     }
 
     private async Task ApplyDxDarkOverrideAsync()