Add NBT support to GRN processing and pricing calculations

Distribution/Models/Enums.cs

@@ -45,5 +45,8 @@ namespace Distribution.Models
     /// </summary>
     public enum InvoiceCreationMode { ModeA, ModeB }
 
+    /// <summary>How a tax applies on a document: not at all, may be left at 0, or must be filled in.</summary>
+    public enum TaxMode { Disabled, Optional, Mandatory }
+
     public enum SerialStatus { InStock, Sold, Returned, Damaged }
 }

Distribution/Models/GoodsReceipt.cs

@@ -36,6 +36,10 @@ namespace Distribution.Models
         [Precision(5, 2)]
         public decimal VatPercent { get; set; }
 
+        /// <summary>GRN-wide default NBT %, applied to any line that doesn't set its own.</summary>
+        [Precision(5, 2)]
+        public decimal NbtPercent { get; set; }
+
         public ICollection<GoodsReceiptItem> Items { get; set; } = [];
     }
 }

Distribution/Models/GoodsReceiptItem.cs

@@ -41,6 +41,9 @@ namespace Distribution.Models
         [Precision(5, 2)]
         public decimal VatPercent { get; set; }
 
+        [Precision(5, 2)]
+        public decimal NbtPercent { get; set; }
+
         /// <summary>Populated when the received item tracks batches and/or expiry dates.</summary>
         public ICollection<GoodsReceiptItemBatch> Batches { get; set; } = [];