Add discoont rule

Backend/ERPCore/Domain/Entities/SalesInvoiceLine.cs

@@ -1,3 +1,5 @@
+using ERPCore.Domain.Enums;
+
 namespace ERPCore.Domain.Entities;
 
 public class SalesInvoiceLine
@@ -22,6 +24,7 @@ public class SalesInvoiceLine
     public decimal UnitPrice { get; set; }
     public decimal BaseCost { get; set; }
     public string PriceSource { get; set; } = string.Empty;
+    public SalesDiscountMode DiscountMode { get; set; } = SalesDiscountMode.Percentage;
     public decimal DiscountPct { get; set; }
     public decimal DiscountAmount { get; set; }
     public decimal NetUnitPrice { get; set; }

Backend/ERPCore/Domain/Entities/SalesSlipLine.cs

@@ -1,3 +1,5 @@
+using ERPCore.Domain.Enums;
+
 namespace ERPCore.Domain.Entities;
 
 public class SalesSlipLine
@@ -22,6 +24,7 @@ public class SalesSlipLine
     public decimal UnitPrice { get; set; }
     public decimal BaseCost { get; set; }
     public string PriceSource { get; set; } = string.Empty;
+    public SalesDiscountMode DiscountMode { get; set; } = SalesDiscountMode.Percentage;
     public decimal DiscountPct { get; set; }
     public decimal DiscountAmount { get; set; }
     public decimal NetUnitPrice { get; set; }

Backend/ERPCore/Domain/Enums/SalesDiscountMode.cs

@@ -0,0 +1,7 @@
+namespace ERPCore.Domain.Enums;
+
+public enum SalesDiscountMode
+{
+    Percentage = 1,
+    FixedAmount = 2
+}