fix(reorder): save layer list AND preview layout immediately at drop; recording save dialog +10% (276→304)

Reorder: OnSceneElementsReordered now calls SaveLayoutNow() (was debounced
ScheduleSave) so a drag-drop persists instantly — one write stores the new
layer list (Source.SortOrder) and each layer's preview geometry (X/Y/W/H) in
the same rows. Reference: WPF ListBox drag-reorder requires an explicit persist
at drop; a debounce window lets a crash lose the drop.

Recording save dialog (RenameRecordingDialog.xaml): height 276→304 so the
Cancel/Save button row is no longer obscured; Save button named
SaveRecordingButton so the sizing test can assert it sits inside the client area.

Tests: deterministic seam test now asserts the dragged layer's geometry (preview
layout) is persisted with the new order; sizing test asserts 304 + textbox and
button-row bottoms within client area. 308/308 green.

RenameRecordingDialog.xaml

@@ -1,7 +1,7 @@
 <Window x:Class="ytLive.RenameRecordingDialog"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        Title="Rename Recording" Height="276" Width="460"
+        Title="Rename Recording" Height="304" Width="460"
         Icon="/ytLive;component/Assets/llamacasty-icon.png"
         WindowStartupLocation="CenterOwner" ResizeMode="NoResize"
         ShowInTaskbar="False" Background="#1a1a2e">
@@ -32,7 +32,7 @@
                     Margin="0,20,0,0">
             <Button Content="Cancel" Click="Cancel_Click"
                     Style="{StaticResource YtButtonSecondary}" Margin="0,0,8,0"/>
-            <Button Content="Save" Click="Save_Click" Style="{StaticResource YtButton}" MinWidth="90"/>
+            <Button Content="Save" Click="Save_Click" Style="{StaticResource YtButton}" MinWidth="90" x:Name="SaveRecordingButton"/>
         </StackPanel>
     </Grid>
 </Window>