fix(docking): address final code quality issues in docking layout

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

@@ -3,6 +3,9 @@ using Microsoft.UI.Xaml.Controls;
 
 namespace Ghost.Editor.View.Controls.Docking;
 
+/// <summary>
+/// Represents a document module in the docking system.
+/// </summary>
 public partial class DockDocument : DockModule
 {
     public static readonly DependencyProperty TitleProperty = DependencyProperty.Register(
@@ -29,6 +32,9 @@ public partial class DockDocument : DockModule
         set => SetValue(ContentProperty, value);
     }
 
+    /// <summary>
+    /// Initializes a new instance of the <see cref="DockDocument"/> class.
+    /// </summary>
     public DockDocument()
     {
         DefaultStyleKey = typeof(DockDocument);

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

@@ -95,22 +95,28 @@ public class DockingLayout : Control
             throw new ArgumentException("targetGroup does not belong to this DockingLayout", nameof(targetGroup));
         }
 
-        if (RootModule == null)
-        {
-            RootModule = new DockPanel();
-        }
-
         if (targetGroup == null)
+        {
+            if (RootModule != null)
             {
                 targetGroup = FindFirstDockGroup(RootModule as DockContainer);
-
                 if (targetGroup == null)
                 {
-                targetGroup = new DockGroup();
-                if (RootModule is DockContainer container)
+                    // Root is not a container, or contains no groups. Wrap it.
+                    var newGroup = new DockGroup();
+                    if (RootModule is DockDocument existingDoc)
                     {
-                    container.AddChild(targetGroup);
+                        RootModule = null; // Detach first
+                        newGroup.AddChild(existingDoc);
                     }
+                    RootModule = newGroup;
+                    targetGroup = newGroup;
+                }
+            }
+            else
+            {
+                targetGroup = new DockGroup();
+                RootModule = targetGroup;
             }
         }
 
@@ -191,8 +197,10 @@ public class DockingLayout : Control
         }
     }
 
-    private static DockGroup? FindFirstDockGroup(DockContainer container)
+    private static DockGroup? FindFirstDockGroup(DockContainer? container)
     {
+        if (container == null) return null;
+
         if (container is DockGroup group)
         {
             return group;