Add user-selectable page size to MassData grid

Users can now choose how many records to display per page in the MassData grid (100, 1,000, 10,000, 100,000, or all). The backend and API client are updated to support nullable skip/take parameters, allowing "all" records to be fetched when desired. The pager and page count calculations are updated to reflect the selected page size, and the pager is hidden if only one page exists. Additional UI and CSS changes provide a combo box for page size selection. The API controller now treats take <= 0 as "no limit."

DbFirst.BlazorWasm/Components/MassDataGrid.razor

@@ -10,6 +10,23 @@
         margin-top: 12px;
         margin-bottom: 16px;
     }
+    .page-size-selector {
+        display: flex;
+        align-items: center;
+        gap: 8px;
+        flex-wrap: nowrap;
+    }
+    .page-size-label {
+        white-space: nowrap;
+    }
+    .page-size-combo {
+        width: 13ch;
+        min-width: 13ch;
+        max-width: 13ch;
+    }
+    .page-size-combo input {
+        text-align: left;
+    }
     .massdata-grid .dxbl-grid-sort-asc,
     .massdata-grid .dxbl-grid-sort-desc {
         display: none;
@@ -75,6 +92,18 @@ else if (items.Count == 0)
 }
 else
 {
+    <div class="mb-3 page-size-selector">
+        <span class="page-size-label">Datensätze je Seite:</span>
+        <DxComboBox Data="@pageSizeOptions"
+                    TData="PageSizeOption"
+                    TValue="int?"
+                    TextFieldName="Text"
+                    ValueFieldName="Value"
+                    Value="@pageSize"
+                    ValueChanged="OnPageSizeChanged"
+                    CssClass="page-size-combo" />
+    </div>
+
     <div class="grid-section">
         <DxGrid Data="@items"
                 TItem="MassDataReadDto"
@@ -83,10 +112,9 @@ else
                 ShowGroupPanel="true"
                 AllowColumnResize="true"
                 PagerVisible="false"
-                PageSize="100"
+                PageSize="@(pageSize ?? 100)"
                 CssClass="mb-3 massdata-grid"
                 EditMode="GridEditMode.PopupEditForm"
-                PopupEditFormCssClass="massdata-edit-popup"
                 PopupEditFormHeaderText="@popupHeaderText"
                 CustomizeEditModel="OnCustomizeEditModel"
                 EditModelSaving="OnEditModelSaving"
@@ -182,24 +210,36 @@ else
             </EditFormTemplate>
         </DxGrid>
 
-        <div class="pager-container">
-            <DxPager PageCount="@pageCount" ActivePageIndex="@pageIndex" ActivePageIndexChanged="OnPageChanged" />
-        </div>
+        @if (pageCount > 1)
+        {
+            <div class="pager-container">
+                <DxPager PageCount="@pageCount" ActivePageIndex="@pageIndex" ActivePageIndexChanged="OnPageChanged" />
+            </div>
+        }
     </div>
 }
 
 @code {
-    private const int PageSize = 100;
     private List<MassDataReadDto> items = new();
     private bool isLoading;
     private string? errorMessage;
     private string? infoMessage;
     private int pageIndex;
     private int pageCount = 1;
+    private int? pageSize = 100;
     private string popupHeaderText = "Edit";
     private EditContext? editContext;
     private ValidationMessageStore? validationMessageStore;
 
+    private readonly List<PageSizeOption> pageSizeOptions = new()
+    {
+        new() { Value = 100, Text = "100" },
+        new() { Value = 1000, Text = "1.000" },
+        new() { Value = 10000, Text = "10.000" },
+        new() { Value = 100000, Text = "100.000" },
+        new() { Value = null, Text = "Alle" }
+    };
+
     private readonly List<BoolFilterOption> statusFilterOptions = new()
     {
         new() { Value = null, Text = "Alle" },
@@ -224,11 +264,12 @@ else
         try
         {
             var total = await Api.GetCountAsync();
-            pageCount = Math.Max(1, (int)Math.Ceiling(total / (double)PageSize));
+            var effectivePageSize = pageSize ?? (total == 0 ? 1 : total);
+            pageCount = Math.Max(1, (int)Math.Ceiling(total / (double)effectivePageSize));
             pageIndex = Math.Clamp(page, 0, pageCount - 1);
 
-            var skip = pageIndex * PageSize;
-            items = await Api.GetAllAsync(skip, PageSize);
+            var skip = pageSize.HasValue ? pageIndex * pageSize.Value : 0;
+            items = await Api.GetAllAsync(skip, pageSize);
         }
         catch (Exception ex)
         {
@@ -246,6 +287,12 @@ else
         await LoadPage(index);
     }
 
+    private async Task OnPageSizeChanged(int? size)
+    {
+        pageSize = size;
+        await LoadPage(0);
+    }
+
     private void SetEditContext(EditContext context)
     {
         if (editContext == context)
@@ -405,4 +452,10 @@ else
         public bool? Value { get; set; }
         public string Text { get; set; } = string.Empty;
     }
+
+    private sealed class PageSizeOption
+    {
+        public int? Value { get; set; }
+        public string Text { get; set; } = string.Empty;
+    }
 }