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/EnvelopeReceiver.cs

@@ -1,21 +1,21 @@
-using System.ComponentModel.DataAnnotations;
+using System;
+using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
 using DigitalData.Core.Abstractions.Interfaces;
 using EnvelopeGenerator.Domain.Interfaces;
 
 #if NETFRAMEWORK
-using System;
 #endif
 
 namespace EnvelopeGenerator.Domain.Entities
 #if NET
     ;
 #elif NETFRAMEWORK
-    {
+{
 #endif
 
 [Table("TBSIG_ENVELOPE_RECEIVER", Schema = "dbo")]
-public class EnvelopeReceiver : IHasEnvelope, IHasReceiver, IEntity
+public class EnvelopeReceiver : IHasEnvelope, IHasReceiver, IEntity, IHasAddedWhen, IHasChangedWhen
 {
     public EnvelopeReceiver()
     {
@@ -42,7 +42,7 @@ public class EnvelopeReceiver : IHasEnvelope, IHasReceiver, IEntity
 
     [Column("COMPANY_NAME", TypeName = "nvarchar(128)")]
     public string
-#if NET
+#if nullable
         ?
 #endif
         CompanyName { get; set; }
@@ -58,7 +58,7 @@ public class EnvelopeReceiver : IHasEnvelope, IHasReceiver, IEntity
     public DateTime AddedWhen { get; set; }
 
     [Column("CHANGED_WHEN", TypeName = "datetime")]
-    public DateTime ChangedWhen { get; set; }
+    public DateTime? ChangedWhen { get; set; }
 
     [Column("PHONE_NUMBER")]
     [StringLength(20)]
@@ -73,14 +73,14 @@ public class EnvelopeReceiver : IHasEnvelope, IHasReceiver, IEntity
 
     [ForeignKey("EnvelopeId")]
     public Envelope
-#if NET
+#if nullable
         ?
 #endif
             Envelope { get; set; }
 
     [ForeignKey("ReceiverId")]
     public Receiver
-#if NET
+#if nullable
         ?
 #endif
             Receiver { get; set; }