feat(docking): implement proportional sizing for docking layout

- Add DockLength property to DockModule to track star weights
- Add SyncLengths() to DockPanel to capture current Grid weights
- Update DockPanel.UpdateLayoutStructure to use DockLength
- Update DockingLayout.SplitGroup to distribute weights when splitting

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

@@ -12,6 +12,11 @@ public abstract class DockModule : Control
     /// </summary>
     public DockContainer? Owner { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets the proportional length (star weight) of this module within its parent panel.
+    /// </summary>
+    public double DockLength { get; set; } = 1.0;
+    
     private DockingLayout? _root;
 
     /// <summary>

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

@@ -45,6 +45,33 @@ public partial class DockPanel : DockContainer
         UpdateLayoutStructure();
     }
 
+    internal void SyncLengths()
+    {
+        if (_grid == null) return;
+        if (Orientation == Orientation.Horizontal)
+        {
+            for (int i = 0; i < Children.Count; i++)
+            {
+                int col = i * 2;
+                if (col < _grid.ColumnDefinitions.Count)
+                {
+                    Children[i].DockLength = _grid.ColumnDefinitions[col].Width.Value;
+                }
+            }
+        }
+        else
+        {
+            for (int i = 0; i < Children.Count; i++)
+            {
+                int row = i * 2;
+                if (row < _grid.RowDefinitions.Count)
+                {
+                    Children[i].DockLength = _grid.RowDefinitions[row].Height.Value;
+                }
+            }
+        }
+    }
+
     internal override void CheckCleanup()
     {
         base.CheckCleanup();
@@ -85,7 +112,7 @@ public partial class DockPanel : DockContainer
         {
             for (int i = 0; i < Children.Count; i++)
             {
-                _grid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });
+                _grid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(Children[i].DockLength, GridUnitType.Star) });
                 var child = Children[i];
                 Grid.SetColumn(child, i * 2);
                 _grid.Children.Add(child);
@@ -103,7 +130,7 @@ public partial class DockPanel : DockContainer
         {
             for (int i = 0; i < Children.Count; i++)
             {
-                _grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
+                _grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(Children[i].DockLength, GridUnitType.Star) });
                 var child = Children[i];
                 Grid.SetRow(child, i * 2);
                 _grid.Children.Add(child);

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

@@ -144,6 +144,7 @@ public partial class DockingLayout : Control
     private void SplitGroup(DockGroup targetGroup, DockDocument doc, DockTarget target)
     {
         var parentPanel = targetGroup.Owner as DockPanel;
+        parentPanel?.SyncLengths(); // Sync before modifying!
 
         var newGroup = new DockGroup();
         newGroup.AddChild(doc);
@@ -156,6 +157,9 @@ public partial class DockingLayout : Control
             var newPanel = new DockPanel { Orientation = orientation };
             RootModule = newPanel;
 
+            targetGroup.DockLength = 1.0;
+            newGroup.DockLength = 1.0;
+
             if (target == DockTarget.Left || target == DockTarget.Top)
             {
                 newPanel.AddChild(newGroup);
@@ -178,7 +182,11 @@ public partial class DockingLayout : Control
 
         if (parentPanel.Orientation == orientation)
         {
-            // Same orientation, just insert
+            // Splitting in the same orientation. Share the length.
+            double halfLength = targetGroup.DockLength / 2.0;
+            targetGroup.DockLength = halfLength;
+            newGroup.DockLength = halfLength;
+
             if (target == DockTarget.Left || target == DockTarget.Top)
             {
                 parentPanel.InsertChild(index, newGroup);
@@ -190,8 +198,13 @@ public partial class DockingLayout : Control
         }
         else
         {
-            // Different orientation, need a new sub-panel
+            // Splitting in opposite orientation. New panel takes the full length.
             var newPanel = new DockPanel { Orientation = orientation };
+            newPanel.DockLength = targetGroup.DockLength;
+
+            targetGroup.DockLength = 1.0;
+            newGroup.DockLength = 1.0;
+
             parentPanel.ReplaceChild(targetGroup, newPanel);
 
             if (target == DockTarget.Left || target == DockTarget.Top)