feat(docking): improve tab management and error handling

Refactored DockGroup to only remove obsolete TabViewItems and restore tab selection more reliably. Updated DockGroup.xaml to enable tab reordering and add-tab button. Switched to CommunityToolkit.WinUI.Controls for GridSplitter and added a style for it. Made DockPanel, DockRegionHighlight, and DockingLayout partial classes. In App.xaml.cs, wrapped initialization in a try-catch to exit on error, and ensured process exit on window close. Improved ProjectBrowser scrollbar behavior and layout settings.

src/Editor/Ghost.Editor/Themes/Generic.xaml

@@ -1,7 +1,7 @@
 <ResourceDictionary
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-    xmlns:controls="using:Microsoft.UI.Xaml.Controls"
+    xmlns:controls="using:CommunityToolkit.WinUI.Controls"
     xmlns:ghost="using:Ghost.Editor.Controls"
     xmlns:local="using:Ghost.Editor.Core">
 
@@ -42,6 +42,11 @@
         <Setter Property="TabWidthMode" Value="Compact" />
     </Style>
     <Style TargetType="NumberBox" />
+    <Style TargetType="controls:GridSplitter">
+        <Setter Property="MinHeight" Value="2" />
+        <Setter Property="MinWidth" Value="2" />
+        <Setter Property="Background" Value="{ThemeResource AcrylicBackgroundFillColorBaseBrush}" />
+    </Style>
 
     <!--  Named Style  -->
     <Style