[Settings] Mica & modern titlebar (#25936)

* Adding Mica

* Working Mica

* Fluent titlebar

* Modern titlebar

* Fixing OOBE

* Fix build issue

* Add missing entry to NOTICE.md

* Update App.xaml.cs

src/settings-ui/Settings.UI/MainWindow.xaml.cs

@@ -220,6 +220,8 @@ namespace Microsoft.PowerToys.Settings.UI
 
             this.InitializeComponent();
 
+            SetTheme(isDark);
+
             // receive IPC Message
             App.IPCMessageReceivedCallback = (string msg) =>
             {
@@ -279,5 +281,10 @@ namespace Microsoft.PowerToys.Settings.UI
         {
             ShellPage.EnsurePageIsSelected();
         }
+
+        private void SetTheme(bool isDark)
+        {
+            shellPage.RequestedTheme = isDark ? ElementTheme.Dark : ElementTheme.Light;
+        }
     }
 }