UI threading work

Hyperbar.Windows/Lifecycles/ConfigurationChangedHandler.cs

@@ -0,0 +1,14 @@
+using Hyperbar.Windows.Controls;
+
+namespace Hyperbar.Windows.Primary;
+
+public class AppConfigurationChangedHandler(DesktopFlyout desktopFlyout,
+    AppConfiguration configuration) :
+    INotificationHandler<ConfigurationChanged<AppConfiguration>>
+{
+    public ValueTask Handle(ConfigurationChanged<AppConfiguration> notification, CancellationToken cancellationToken)
+    {
+        desktopFlyout.Placement = configuration.Placement;
+        return ValueTask.CompletedTask;
+    }
+}