- Introduced AnnotationCreateDto for creation-specific properties
- AnnotationDto now inherits from AnnotationCreateDto and includes Id, AddedWhen, ChangedWhen, and ChangedWho
- Added Type property to AnnotationCreateDto
- remove CreateAnnotationCommand
- Introduced new record `PsPdfKitAnnotation` to encapsulate both Instant and Structured annotation data
- Updated `DocSignedNotification` to use `PsPdfKitAnnotation` instead of `ExpandoObject Annotations`
- Modified extension methods to accept and map `PsPdfKitAnnotation`
- Added reference to `EnvelopeGenerator.Application.Annotations.Commands` for `CreateAnnotationCommand`
- Implemented AnnotationHandler to process DocSignedNotification events
- Sends CreateAnnotationCommand via MediatR with envelope, receiver, and annotations data
