Handle envelope type with framework-specific properties

Add conditional logic to map "ENVELOPE_TYPE" to either an int? EnvelopeTypeId (for .NET Framework) or a type-safe EnvelopeSigningType SigningType (for .NET), supporting both legacy and modern approaches.

EnvelopeGenerator.Domain/Entities/Envelope.cs

@@ -104,8 +104,20 @@ public class Envelope
     [Column("REMINDER_INTERVAL_DAYS")]
     public int? ReminderIntervalDays { get; set; }
 
+#if NETFRAMEWORK
     [Column("ENVELOPE_TYPE")]
     public int? EnvelopeTypeId { get; set; }
+#elif NET
+
+    private EnvelopeSigningType _signingType = EnvelopeSigningType.WetSignature;
+
+    [Column("ENVELOPE_TYPE")]
+    public EnvelopeSigningType SigningType 
+    { 
+        get => _signingType;
+        set => _signingType = value.Normalize();
+    }
+#endif
 
     [Column("CERTIFICATION_TYPE")]
     public int? CertificationType { get; set; }