refactor: Plattform-spezifische Anpassungen an der Receiver-Klasse

- `NotMapped` Properties nur für NETFRAMEWORK verfügbar gemacht
- Klasse und Namespaces für NET- und NETFRAMEWORK-Bedingungen angepasst
- Redundant in NET definierten Code entfernt

EnvelopeGenerator.Domain/Entities/Receiver.cs

@@ -7,10 +7,15 @@ using System.Collections.Generic;
 #endif
 
 namespace EnvelopeGenerator.Domain.Entities
-{
-    [Table("TBSIG_RECEIVER", Schema = "dbo")]
-    public class Receiver
+#if NET
+    ;
+#elif NETFRAMEWORK
     {
+#endif
+
+[Table("TBSIG_RECEIVER", Schema = "dbo")]
+public class Receiver
+{
     [Key]
     [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
     [Column("GUID")]
@@ -37,6 +42,7 @@ namespace EnvelopeGenerator.Domain.Entities
 
     public List<EnvelopeReceiver> EnvelopeReceivers { get; set; }
 
+#if NETFRAMEWORK
     [NotMapped]
     public string Name { get; set; }
 
@@ -86,5 +92,9 @@ namespace EnvelopeGenerator.Domain.Entities
     {
         return EmailAddress.ToUpperInvariant().GetChecksum();
     }
-    }
+#endif
 }
+
+#if NETFRAMEWORK
+    }
+#endif