Add NBT support to GRN processing and pricing calculations

Distribution/Features/Grn/GrnDTOs.cs

@@ -20,7 +20,9 @@ public record GrnItemRequest(
     decimal? DiscountPercent = null,
     decimal? VatPercent = null,
     // Free-issue units: stocked but not costed. Serial/batch entries must cover accepted + free.
-    int FreeQuantity = 0);
+    int FreeQuantity = 0,
+    // Ignored when NBT is disabled in configuration; null falls back to the GRN-wide percentage.
+    decimal? NbtPercent = null);
 
 public record CreateGrnRequest(
     Guid WarehouseId,
@@ -29,7 +31,8 @@ public record CreateGrnRequest(
     Guid? ReceivedByUserId = null,
     // GRN-wide defaults for lines that don't set their own.
     decimal? DiscountPercent = null,
-    decimal? VatPercent = null);
+    decimal? VatPercent = null,
+    decimal? NbtPercent = null);
 
 public record CreateFlatGrnRequest(
     Guid PurchaseOrderId,
@@ -38,7 +41,8 @@ public record CreateFlatGrnRequest(
     // TEMPORARY: required while auth doesn't resolve a logged-in user server-side — see testbug.md #28.
     Guid? ReceivedByUserId = null,
     decimal? DiscountPercent = null,
-    decimal? VatPercent = null);
+    decimal? VatPercent = null,
+    decimal? NbtPercent = null);
 
 /// <summary>A goods receipt with no purchase order. SupplierId is optional.</summary>
 public record CreateDirectGrnRequest(
@@ -48,7 +52,8 @@ public record CreateDirectGrnRequest(
     // TEMPORARY: required while auth doesn't resolve a logged-in user server-side — see testbug.md #28.
     Guid? ReceivedByUserId = null,
     decimal? DiscountPercent = null,
-    decimal? VatPercent = null);
+    decimal? VatPercent = null,
+    decimal? NbtPercent = null);
 
 public record GrnBatchLineResponse(string? BatchNumber, DateTime? ExpiryDate, int Quantity);
 
@@ -71,7 +76,9 @@ public record GrnItemResponse(
     decimal VatAmount,
     // Gross - discount + VAT.
     decimal LineTotal,
-    int FreeQuantity);
+    int FreeQuantity,
+    decimal NbtPercent,
+    decimal NbtAmount);
 
 public record GrnResponse(
     Guid Id,
@@ -89,7 +96,9 @@ public record GrnResponse(
     // Sum of line gross amounts.
     decimal SubTotal,
     decimal DiscountAmount,
-    // SubTotal - DiscountAmount (the base VAT is charged on).
+    // SubTotal - DiscountAmount (the base NBT is charged on; VAT is charged on this plus NBT).
     decimal TaxableAmount,
     decimal VatAmount,
-    decimal TotalAmount);
+    decimal TotalAmount,
+    decimal NbtPercent,
+    decimal NbtAmount);