Add scheme data model and migrations

Distribution/Models/SchemeRedemption.cs

@@ -0,0 +1,36 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class SchemeRedemption
+    {
+        public Guid Id { get; set; } = Guid.NewGuid();
+
+        public Guid FK_SchemeId { get; set; }
+        [ForeignKey("FK_SchemeId")]
+        public Scheme Scheme { get; set; }
+
+        public Guid? FK_OrderId { get; set; }
+        [ForeignKey("FK_OrderId")]
+        public Order? Order { get; set; }
+
+        /// <summary>Placeholder for the future field-invoice module — no FieldInvoice entity exists yet.</summary>
+        public Guid? FieldInvoiceId { get; set; }
+
+        public decimal? DiscountAmount { get; set; }
+
+        public Guid? FK_FreeItemId { get; set; }
+        [ForeignKey("FK_FreeItemId")]
+        public Item? FreeItem { get; set; }
+
+        public decimal? FreeQty { get; set; }
+
+        /// <summary>
+        /// Cost price of the free item snapshotted at redemption time, so getSchemeROI stays
+        /// accurate even after the item's cost price later changes.
+        /// </summary>
+        public decimal? FreeItemCostValue { get; set; }
+
+        public DateTime RedeemedAt { get; set; } = DateTime.Now;
+    }
+}