feat: single view trial.

demo/Ursa.Demo/Views/SingleView.axaml

@@ -1,4 +1,4 @@
-<UserControl xmlns="https://github.com/avaloniaui"
+<u:UrsaView xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
@@ -7,8 +7,8 @@
              mc:Ignorable="d" d:DesignWidth="800"
              d:DesignHeight="450"
              x:Class="Ursa.Demo.Views.SingleView">
-    <Panel>
-        <views:MainView/>
-        <u:OverlayDialogHost/>
-    </Panel>
-</UserControl>
+    <u:UrsaView.RightContent>
+        <views:TitleBarRightContent/>
+    </u:UrsaView.RightContent>
+    <views:MainView/>
+</u:UrsaView>