Added a new `SignatureDto` record to represent captured signatures with metadata, including properties like `ElementId`, `DataUrl`, `FullName`, `Position`, and `Place`. Updated `SigningCommand` to include a `Signatures` property for handling multiple signatures, deprecating `PsPdfKitAnnotation`.
Introduced a `MappingProfile` class to map `SignatureDto` to `DocReceiverElement` using AutoMapper. Added necessary `using` directives to support the new mapping configuration.
