ui(settings): 20px right gutter on the drawer, rail tabs centred on the preview

Two build-1047 notes. The settings content gets a 20px right margin (plus 4 left) inside the
scroll viewer, so text and controls stop running into the panel edge and the scrollbar has
somewhere to live. The rail tab stack is VerticalAlignment=Center instead of Stretch, so the
whole group of tabs sits centred against the preview rather than hanging from the top.

Controls/PreviewPane.xaml

@@ -941,7 +941,7 @@
                                 </Grid>
                             </Border>
                             <!-- The stacked white tabs -->
-                            <StackPanel Orientation="Vertical" HorizontalAlignment="Right" VerticalAlignment="Stretch">
+                            <StackPanel Orientation="Vertical" HorizontalAlignment="Right" VerticalAlignment="Center">
                                 <!-- Settings: the first tab, orange, gear only (creator ruling
                                      2026-11-01). A left click opens the Settings DRAWER immediately
                                      — same behaviour as the other rail tabs. The app menu (Report

Controls/SettingsDrawer.xaml

@@ -11,7 +11,7 @@
 
          Categories are headings; their controls are indented under them (Zoom is one). -->
     <ScrollViewer VerticalScrollBarVisibility="Auto" HorizontalScrollBarVisibility="Disabled">
-        <StackPanel Margin="0,0,4,0">
+        <StackPanel Margin="4,0,20,0">
 
             <!-- ═══ RECORDINGS ═══ -->
             <TextBlock Text="Recordings" Style="{StaticResource SectionHeader}" Margin="0,0,0,4"/>