Update grid docs, metadata, and add new screenshots

Standardize XML docs for Blazor grid parameters, add API metadata attributes, and improve type safety by making parameters nullable where appropriate. Remove obsolete PaginationAlignment parameter. Update demo screenshot references and add new image files for grid features, nested grids, and translations. No functional changes; all updates are documentation, API surface, or demo assets.

Author: gvreddy04

BlazorBootstrap.Demo.RCL/Constants/DemoScreenshotSrcConstants.cs

@@ -50,15 +50,15 @@ public class DemoScreenshotSrcConstants
 
     #region Grid
     public const string Demos_URL_Grid_Prefix = DemoScreenshotSrcPrefix + "grid.png";
-    public const string Demos_URL_Grid_Overview = DemoScreenshotSrcPrefix + "home.png";
+    public const string Demos_URL_Grid_Overview = DemoScreenshotSrcPrefix + "grid_fixed_header_freeze_columns.png";
     public const string Demos_URL_Grid_Alignment = DemoScreenshotSrcPrefix + "home.png";
     public const string Demos_URL_Grid_CustomCSSClass = DemoScreenshotSrcPrefix + "home.png";
     public const string Demos_URL_Grid_DataBinding = DemoScreenshotSrcPrefix + "home.png";
     public const string Demos_URL_Grid_DetailView = DemoScreenshotSrcPrefix + "home.png";
     public const string Demos_URL_Grid_Events = DemoScreenshotSrcPrefix + "home.png";
     public const string Demos_URL_Grid_Filters = DemoScreenshotSrcPrefix + "home.png";
-    public const string Demos_URL_Grid_FixedHeader = DemoScreenshotSrcPrefix + "home.png";
-    public const string Demos_URL_Grid_FreezeColumns = DemoScreenshotSrcPrefix + "home.png";
+    public const string Demos_URL_Grid_FixedHeader = DemoScreenshotSrcPrefix + "grid_fixed_header_freeze_columns.png";
+    public const string Demos_URL_Grid_FreezeColumns = DemoScreenshotSrcPrefix + "grid_fixed_header_freeze_columns.png";
     public const string Demos_URL_Grid_Settings = DemoScreenshotSrcPrefix + "home.png";
     public const string Demos_URL_Grid_NestedGrid = DemoScreenshotSrcPrefix + "home.png";
     public const string Demos_URL_Grid_Paging = DemoScreenshotSrcPrefix + "home.png";