Introduced interfaces for audit fields (AddedWhen, ChangedWhen, ChangedWho, AddedWho) and updated domain entities to implement them. Adjusted properties for consistency and nullability. Updated MappingProfile to map audit fields between DTOs and entities. Improves auditability and standardization across the domain model.
Added a new nullable ReceiverSignature property to the RemoveSignatureNotification record
to support handling receiver-specific signature removal events.
Added full implementation for CreateAnnotationCommand and its handler:
- Introduced `PSPDFKitInstantJSON` property to the command
- Injected repositories for `Signature` and `Annotation`
- Implemented query filtering for Envelope and Receiver
- Added annotation creation from parsed PSPDFKit JSON
- Created helper method `ParsePSPDFKitInstantJSON` for JSON parsing
