fix(dock): inside the work area, bottom edge aligned with the layers panel

The dock was a sibling row BELOW the whole work area, so it could not line up with the layers
panel and read as sitting under it. It now lives in the work-area grid (preview column, bottom
row), and the left panel spans content + dock rows — both columns end on the same line, which is
what the creator asked for.

No behaviour change; placement only.

MainWindow.xaml

@@ -75,6 +75,9 @@
             <Grid.RowDefinitions>
                 <RowDefinition Height="Auto"/>
                 <RowDefinition Height="*"/>
+                <!-- the dock lives INSIDE the work area so its bottom edge lines up with the
+                     layers panel (creator, 2026-10-30) -->
+                <RowDefinition Height="Auto"/>
             </Grid.RowDefinitions>
             <Grid.ColumnDefinitions>
                 <ColumnDefinition Width="360"/>
@@ -140,17 +143,18 @@
             <!-- LEFT PANEL: one panel, two states.
                  Offline (edit mode): LAYERS + PROPERTIES
                  Live/Recording: YouTube Live Chat -->
-            <controls:LeftPanel x:Name="LeftPanel" Grid.Row="1" Grid.Column="0"/>
+            <controls:LeftPanel x:Name="LeftPanel" Grid.Row="1" Grid.Column="0" Grid.RowSpan="2"/>
 
 
             <!-- CENTER: Preview Area -->
             <controls:PreviewPane x:Name="PreviewPane" Grid.Row="1" Grid.Column="1"/>
+
+            <!-- The dock starts where the layers panel ends and shares its bottom edge. -->
+            <controls:AudioDock x:Name="AudioDock" Grid.Row="2" Grid.Column="1"/>
         </Grid>
 
 
-        <!-- The dock starts where the layers panel ends: it is a preview-column control, not
+
-             a full-width footer (creator, 2026-10-30). -->
-        <controls:AudioDock Grid.Row="3" Grid.Column="1"/>
         <!-- ═══ OVERLAY: Settings / Bug / Feature / About ═══ -->
         <controls:OverlayHost Grid.RowSpan="3"/>