Remove unused bandEditorExpanded field from BandGridBase

The protected bool bandEditorExpanded, which tracked the expansion
state of the band editor, has been removed from BandGridBase<TItem>
as it is no longer used. This helps clean up unused state from
the component.

DbFirst.BlazorWebApp/Components/BandGridBase.cs

@@ -21,7 +21,6 @@ public abstract class BandGridBase<TItem> : ComponentBase
     protected Dictionary<string, ColumnDefinition> columnLookup = new();
     protected string? layoutUser;
     protected bool gridLayoutApplied;
-    protected bool bandEditorExpanded;
     protected IGrid? gridRef;
 
     // --- SizeMode ---