Add audit interfaces and fields to domain entities

Introduced interfaces for audit fields (AddedWhen, ChangedWhen, ChangedWho, AddedWho) and updated domain entities to implement them. Adjusted properties for consistency and nullability. Updated MappingProfile to map audit fields between DTOs and entities. Improves auditability and standardization across the domain model.

EnvelopeGenerator.Domain/Entities/Signature.cs

@@ -1,9 +1,9 @@
-using EnvelopeGenerator.Domain.Interfaces;
+using System;
+using EnvelopeGenerator.Domain.Interfaces;
 using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
 #if NETFRAMEWORK
-using System;
 using System.Collections.Generic;
 #endif
 
@@ -11,11 +11,11 @@ namespace EnvelopeGenerator.Domain.Entities
 #if NET
     ;
 #elif NETFRAMEWORK
-    {
+{
 #endif
 
 [Table("TBSIG_DOCUMENT_RECEIVER_ELEMENT", Schema = "dbo")]
-public class Signature : ISignature, IHasReceiver
+public class Signature : ISignature, IHasReceiver, IHasAddedWhen, IHasChangedWhen, IHasChangedWho
 {
     public Signature()
     {
@@ -92,14 +92,14 @@ public class Signature : ISignature, IHasReceiver
     [Required]
     [Column("ADDED_WHEN", TypeName = "datetime")]
     [DefaultValue("GETDATE()")]
-    public DateTime? AddedWhen { get; set; }
+    public DateTime AddedWhen { get; set; }
 
     [Column("CHANGED_WHEN", TypeName = "datetime")]
     public DateTime? ChangedWhen { get; set; }
 
     [Column("CHANGED_WHO", TypeName = "nvarchar(100)")]
     public string
-#if NET
+#if nullable
         ?
 #endif
         ChangedWho { get; set; }
@@ -109,13 +109,13 @@ public class Signature : ISignature, IHasReceiver
 
     [ForeignKey("ReceiverId")]
     public virtual Receiver
-#if NET
+#if nullable
         ?
 #endif
         Receiver { get; set; }
 
     public virtual IEnumerable<ElementAnnotation>
-#if NET
+#if nullable
         ?
 #endif
         Annotations { get; set; }