Give the application a settings area built from what really exists

src/DodoSSH.Client.App/Views/SettingsTitleBar.axaml

@@ -0,0 +1,79 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:DodoSSH.Client.Shell.ViewModels"
+             x:Class="DodoSSH.Client.App.Views.SettingsTitleBar"
+             x:DataType="vm:MainWindowViewModel">
+
+  <!--
+    v5c: settings mode's own titlebar — SettingsNav.dc.html and the four Settings-*.dc.html sources all draw
+    the same 53px bar: "Back to application" on the left, in place of the wordmark and the search box, and
+    the same three window-control glyphs on the right TitleBar.axaml already draws.
+
+    A separate control rather than a variant of TitleBar itself, on the same reasoning SessionHeader and
+    SessionStatusBar are their own files: nothing here can be measured by a test that hosts the real window,
+    and a control that is either "the wordmark bar" or "the settings bar" depending on a bound flag would be
+    two controls wearing one name. The dragging, maximising and closing logic is duplicated from TitleBar's
+    own code-behind rather than shared through a base class — four short handlers, and the day one of the two
+    bars needs its own window behaviour a shared base would have to be pulled apart first.
+
+    v5c-3: two back buttons rather than one whose text and command a converter swaps, toggled by
+    MainWindowViewModel.IsImportOpen — Import.dc.html draws the same 53px bar with "Back to preferences" in
+    place of "Back to application" while the importer is up, and CloseImportCommand closes it without leaving
+    settings mode, unlike LeaveSettingsCommand.
+  -->
+
+  <Border Height="53" Background="{StaticResource DeepChrome}"
+          PointerPressed="OnDrag" DoubleTapped="OnToggleMaximised">
+
+    <Grid ColumnDefinitions="*,Auto" Margin="26,0,20,0">
+
+      <Button Grid.Column="0" Classes="flat" HorizontalAlignment="Left"
+              IsVisible="{Binding !IsImportOpen}"
+              Command="{Binding LeaveSettingsCommand}"
+              ToolTip.Tip="Back to the screen you were on before opening Settings">
+        <StackPanel Orientation="Horizontal" Spacing="12" VerticalAlignment="Center">
+          <TextBlock FontFamily="{StaticResource IconFont}" Text="&#xE5C4;" FontSize="17"
+                     Foreground="{StaticResource TextFaint}" VerticalAlignment="Center" />
+          <TextBlock Text="Back to application" FontSize="13" FontWeight="SemiBold"
+                     Foreground="{StaticResource Text}" VerticalAlignment="Center" />
+        </StackPanel>
+      </Button>
+
+      <Button Grid.Column="0" Classes="flat" HorizontalAlignment="Left"
+              IsVisible="{Binding IsImportOpen}"
+              Command="{Binding CloseImportCommand}"
+              ToolTip.Tip="Back to preferences, without leaving Settings">
+        <StackPanel Orientation="Horizontal" Spacing="12" VerticalAlignment="Center">
+          <TextBlock FontFamily="{StaticResource IconFont}" Text="&#xE5C4;" FontSize="17"
+                     Foreground="{StaticResource TextFaint}" VerticalAlignment="Center" />
+          <TextBlock Text="Back to preferences" FontSize="13" FontWeight="SemiBold"
+                     Foreground="{StaticResource Text}" VerticalAlignment="Center" />
+        </StackPanel>
+      </Button>
+
+      <!-- The window controls, identical to TitleBar's own — see the remark above on why they are repeated. -->
+      <StackPanel Grid.Column="1" Orientation="Horizontal" Spacing="2">
+        <Button Classes="flat" Width="26" Height="24" Click="OnMinimise"
+                ToolTip.Tip="Minimise">
+          <TextBlock FontFamily="{StaticResource IconFont}" Text="&#xE15B;" FontSize="14"
+                     Foreground="{StaticResource TextFaint}"
+                     HorizontalAlignment="Center" VerticalAlignment="Center" />
+        </Button>
+        <Button Classes="flat" Width="26" Height="24" Click="OnToggleMaximised"
+                ToolTip.Tip="Maximise">
+          <TextBlock FontFamily="{StaticResource IconFont}" Text="&#xE3C6;" FontSize="13"
+                     Foreground="{StaticResource TextFaint}"
+                     HorizontalAlignment="Center" VerticalAlignment="Center" />
+        </Button>
+        <Button Classes="flat close" Width="26" Height="24" Click="OnClose"
+                ToolTip.Tip="Close DodoSSH. This ends every shell it has open.">
+          <TextBlock FontFamily="{StaticResource IconFont}" Text="&#xE5CD;" FontSize="14"
+                     HorizontalAlignment="Center" VerticalAlignment="Center" />
+        </Button>
+      </StackPanel>
+
+    </Grid>
+
+  </Border>
+
+</UserControl>