Updated `using` directives to include `DigitalData.Core.Exceptions` for enhanced exception handling. Updated the `[Obsolete]` attribute message to reflect PSPDFKit library deprecation. Renamed `cancellationToken` to `cancel` for consistency.
Added validation to ensure `PsPdfKitAnnotation` is only supported for the `LegacyWeb` receiver type. Introduced stricter checks for missing or invalid annotation data, throwing `BadRequestException` when necessary. Updated `await next` calls to use the renamed parameter.
These changes improve code clarity, enforce stricter validation, and enhance error handling.
