Move ReadOnly property from Envelope to EnvelopeDto

The ReadOnly property logic was shifted from the Envelope entity
to the EnvelopeDto record, ensuring that read-only status is
determined at the DTO layer rather than in the data model.

EnvelopeGenerator.Application/Common/Dto/EnvelopeDto.cs

@@ -74,6 +74,11 @@ public record EnvelopeDto
     /// </summary>
     public int? EnvelopeTypeId { get; set; }
 
+    /// <summary>
+    /// 
+    /// </summary>
+    public bool ReadOnly => EnvelopeTypeId == 2;
+
     /// <summary>
     /// 
     /// </summary>