Moved header into ListView's Padding.

Refactored the AddHeaders method to be an inline local function
within AddListView, improving modularity and encapsulation.
Removed the original AddHeaders implementation and its call
from the constructor. The new AddHeaders method is conditionally
invoked when _applicationData.MinUI is false.

Updated the Y positioning of _listView to use _filterErrorView
instead of _filterLabel. Adjusted _listView padding and scrollbar
position to integrate the header. Changed MARGIN_LEFT constant
from 1 to 0 to refine UI layout.

Author: tig

src/Microsoft.PowerShell.ConsoleGuiTools/OutGridViewWindow.cs

@@ -23,7 +23,7 @@ namespace Microsoft.PowerShell.ConsoleGuiTools;
 internal sealed class OutGridViewWindow : Window
 {
     private const string FILTER_LABEL = "_Filter";
-    private const int MARGIN_LEFT = 1;
+    private const int MARGIN_LEFT = 0;
     private const int CHECK_WIDTH = 2;
 
     private Label? _filterLabel;
@@ -71,7 +71,6 @@ public OutGridViewWindow(ApplicationData applicationData)
         if (!_applicationData.MinUI)
         {
             AddFilter();
-            AddHeaders();
         }
 
         AddListView();
@@ -368,31 +367,6 @@ private void AddFilter()
         _filterField.CursorPosition = _filterField.Text.Length;
     }
 
-    /// <summary>
-    ///     Adds the column header label and separator line to the window.
-    /// </summary>
-    private void AddHeaders()
-    {
-        _header = new View
-        {
-            Y = _applicationData.MinUI ? 0 : Pos.Bottom(_filterErrorView!),
-            Height = 1,
-            Width = Dim.Auto(DimAutoStyle.Text)
-        };
-        Add(_header);
-
-        if (!_applicationData.MinUI)
-        {
-            var headerLine = new Line
-            {
-                X = MARGIN_LEFT,
-                Y = Pos.Bottom(_header),
-                Width = Dim.Fill(MARGIN_LEFT)
-            };
-            Add(headerLine);
-        }
-    }
-
     /// <summary>
     ///     Adds the main list view control to the window with configured selection behavior.
     /// </summary>
@@ -402,7 +376,7 @@ private void AddListView()
         {
             Source = _inputSource,
             X = MARGIN_LEFT,
-            Y = !_applicationData.MinUI ? Pos.Bottom(_filterLabel!) + 2 : 1,
+            Y = !_applicationData.MinUI ? Pos.Bottom(_filterErrorView!) : 1,
             Width = Dim.Fill(),
             Height = Dim.Fill(1),
             AllowsMarking = _applicationData.OutputMode != OutputModeOption.None,
@@ -414,9 +388,49 @@ private void AddListView()
 
         _listView.KeyBindings.Remove(Key.A.WithCtrl);
 
+        if (!_applicationData.MinUI)
+        {
+            AddHeaders();
+        }
+
         Add(_listView);
+        return;
+            
+        void AddHeaders()
+        {
+            _header = new View
+            {
+                //Y = _applicationData.MinUI ? 0 : Pos.Bottom(_filterErrorView!),
+                Height = 1,
+                Width = Dim.Auto(DimAutoStyle.Text)
+            };
+            _header.GettingAttributeForRole += HeaderOnGettingAttributeForRole;
+
+            _listView.ViewportChanged += ListViewOnViewportChanged;
+
+            _listView.Padding!.Thickness = _listView.Padding.Thickness with { Top = 1 };
+            _listView!.Padding!.Add(_header);
+            _listView.VerticalScrollBar.Y = 1;
+            return;
+
+            void ListViewOnViewportChanged(object? sender, DrawEventArgs e)
+            {
+                _header.Viewport = _header.Viewport with { X = _listView.Viewport.X };
+            }
+
+            void HeaderOnGettingAttributeForRole(object? sender, VisualRoleEventArgs e)
+            {
+                if (e.Role == VisualRole.Normal)
+                {
+                    e.Result = e.Result!.Value with { Style = TextStyle.Underline };
+                    e.Handled = true;
+                }
+            }
+        }
     }
 
+
+
     /// <summary>
     ///     Adds the status bar with keyboard shortcuts to the window.
     /// </summary>