Introduced the IsReadAndSign method to IEnvelope extensions, which returns true when EnvelopeTypeId is not 2. This allows clear differentiation between "Read and Sign" and "Read and Confirm" envelope types.
Introduced the IEnvelope interface with an EnvelopeTypeId property in the new EnvelopeGenerator.Domain.Interfaces namespace. Added the EnvelopeExtensions static class with an IsReadAndConfirm extension method to check if EnvelopeTypeId equals 2.
