PivotDataGrid dynamic data support

Schema-less datasets are common when data comes from external APIs. This demo shows how to build a pivot table on top of IDictionary<string, object> records without defining C# models.

The example generates 200 rows with dynamic columns (year, region, category, product, quantity, unit price, discount, total sales) and uses PropertyAccess.GetDynamicPropertyExpression to configure pivot rows, columns, and aggregates at runtime while enabling totals, drill-down, filtering, sorting, and field picking.