fix(docking): address code quality issues in DockingLayout and FloatingWindow

src/Editor/Ghost.Editor/View/Controls/Docking/DockingLayout.cs

@@ -30,6 +30,7 @@ public class DockingLayout : Control
 
     private Canvas? _overlayCanvas;
     private DockRegionHighlight? _highlight;
+    private readonly List<FloatingWindow> _floatingWindows = new();
 
     public DockingLayout()
     {
@@ -113,30 +114,17 @@ public class DockingLayout : Control
     private void SplitGroup(DockGroup targetGroup, DockDocument doc, DockTarget target)
     {
         var parentPanel = targetGroup.Owner as DockPanel;
+
+        if (parentPanel == null)
+        {
+            throw new InvalidOperationException("targetGroup must be owned by a DockPanel to be split.");
+        }
+
         var newGroup = new DockGroup();
         newGroup.AddChild(doc);
 
         var orientation = (target == DockTarget.Left || target == DockTarget.Right) ? Orientation.Horizontal : Orientation.Vertical;
 
-        if (parentPanel == null)
-        {
-            // targetGroup is the root
-            var newPanel = new DockPanel { Orientation = orientation };
-            RootPanel = newPanel;
-
-            if (target == DockTarget.Left || target == DockTarget.Top)
-            {
-                newPanel.AddChild(newGroup);
-                newPanel.AddChild(targetGroup);
-            }
-            else
-            {
-                newPanel.AddChild(targetGroup);
-                newPanel.AddChild(newGroup);
-            }
-        }
-        else
-        {
         int index = parentPanel.Children.IndexOf(targetGroup);
 
         if (parentPanel.Orientation == orientation)
@@ -169,7 +157,6 @@ public class DockingLayout : Control
             }
         }
     }
-    }
 
     private static DockGroup? FindFirstDockGroup(DockContainer container)
     {
@@ -262,6 +249,8 @@ public class DockingLayout : Control
     internal void CreateFloatingWindow(DockDocument doc)
     {
         var window = new FloatingWindow(doc);
+        _floatingWindows.Add(window);
+        window.Closed += (s, e) => _floatingWindows.Remove(window);
         window.Activate();
     }
 }

src/Editor/Ghost.Editor/View/Controls/Docking/FloatingWindow.cs

@@ -2,10 +2,19 @@ using Microsoft.UI.Xaml;
 
 namespace Ghost.Editor.View.Controls.Docking;
 
+/// <summary>
+/// A floating window that contains a docking layout.
+/// </summary>
 public class FloatingWindow : Window
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="FloatingWindow"/> class with the specified document.
+    /// </summary>
+    /// <param name="document">The document to display in the floating window.</param>
     public FloatingWindow(DockDocument document)
     {
+        ArgumentNullException.ThrowIfNull(document);
+
         var layout = new DockingLayout();
         var group = new DockGroup();
         group.AddChild(document);