Refactor grid logic into BandGridBase<TItem> base class

Move shared state and methods from CatalogsGrid and MassDataGrid into BandGridBase<TItem>. This centralizes edit context handling, validation, popup header logic, row editing/deleting, and layout feedback, reducing duplication and improving maintainability. Individual grid components now only override OnEditFieldChanged for custom validation.

DbFirst.BlazorWebApp/Components/BandGridBase.cs

@@ -2,6 +2,7 @@
 using DbFirst.BlazorWebApp.Services;
 using DevExpress.Blazor;
 using Microsoft.AspNetCore.Components;
+using Microsoft.AspNetCore.Components.Forms;
 using Microsoft.AspNetCore.Components.Rendering;
 
 namespace DbFirst.BlazorWebApp.Components;
@@ -27,6 +28,15 @@ public abstract class BandGridBase<TItem> : ComponentBase
     protected SizeMode _sizeMode = SizeMode.Medium;
     protected static readonly List<SizeMode> _sizeModes = Enum.GetValues<SizeMode>().ToList();
 
+    protected string? errorMessage;
+    protected string? infoMessage;
+    protected bool isLoading;
+    protected bool hasLoaded;
+    protected EditContext? editContext;
+    protected ValidationMessageStore? validationMessageStore;
+    protected string popupHeaderText = "Edit";
+    protected int _focusedVisibleIndex;
+
     private const string LayoutType = "GRID_BANDS";
 
     // --- Lifecycle ---
@@ -216,4 +226,53 @@ public abstract class BandGridBase<TItem> : ComponentBase
             builder.AddAttribute(seq++, "ReadOnly", true);
         builder.CloseComponent();
     }
+
+    protected void SetEditContext(EditContext context)
+    {
+        if (editContext == context) return;
+        if (editContext != null)
+            editContext.OnFieldChanged -= OnEditFieldChanged;
+        editContext = context;
+        validationMessageStore = new ValidationMessageStore(editContext);
+        editContext.OnFieldChanged += OnEditFieldChanged;
+    }
+
+    protected virtual void OnEditFieldChanged(object? sender, FieldChangedEventArgs e)
+    {
+        validationMessageStore?.Clear();
+        editContext?.NotifyValidationStateChanged();
+    }
+
+    protected void SetPopupHeaderText(bool isNew) => popupHeaderText = isNew ? "Neu" : "Edit";
+
+    protected async Task EditFocusedRow()
+        => await gridRef!.StartEditRowAsync(_focusedVisibleIndex);
+
+    protected Task DeleteFocusedRow()
+    {
+        gridRef!.ShowRowDeleteConfirmation(_focusedVisibleIndex);
+        return Task.CompletedTask;
+    }
+
+    protected async Task SaveLayoutWithFeedbackAsync()
+    {
+        try
+        {
+            await SaveLayoutAsync();
+            infoMessage = "Layout gespeichert.";
+            errorMessage = null;
+        }
+        catch (Exception ex)
+        {
+            errorMessage = $"Layout konnte nicht gespeichert werden: {ex.Message}";
+        }
+    }
+
+    protected async Task ResetLayoutWithFeedbackAsync()
+    {
+        await ResetLayoutAsync();
+        infoMessage = "Layout zurückgesetzt.";
+        errorMessage = null;
+    }
+
 }