Add GRN batch and serial tracking

Distribution/Models/GoodsReceiptItem.cs

@@ -8,14 +8,26 @@ namespace Distribution.Models
         [ForeignKey("FK_GoodsReceiptId")]
         public GoodsReceipt GoodsReceipt { get; set; }
 
-        public Guid FK_PurchaseOrderItemId { get; set; }
+        /// <summary>Null for a direct receipt line (no purchase order); FK_ItemId is set instead.</summary>
+        public Guid? FK_PurchaseOrderItemId { get; set; }
         [ForeignKey("FK_PurchaseOrderItemId")]
-        public PurchaseOrderItem PurchaseOrderItem { get; set; }
+        public PurchaseOrderItem? PurchaseOrderItem { get; set; }
+
+        /// <summary>Set for direct receipt lines. PO-based lines resolve the item through PurchaseOrderItem.</summary>
+        public Guid? FK_ItemId { get; set; }
+        [ForeignKey("FK_ItemId")]
+        public Item? Item { get; set; }
 
         /// <summary>Added to warehouse stock.</summary>
         public int AcceptedQuantity { get; set; }
 
         /// <summary>Damaged/short at receipt, not added to stock.</summary>
         public int RejectedQuantity { get; set; } = 0;
+
+        /// <summary>Populated when the received item tracks batches and/or expiry dates.</summary>
+        public ICollection<GoodsReceiptItemBatch> Batches { get; set; } = [];
+
+        /// <summary>Populated when the received item tracks serial numbers.</summary>
+        public ICollection<GoodsReceiptItemSerial> Serials { get; set; } = [];
     }
 }