Refactored `DocumentService.GetDocumentAsync` to throw
`HttpRequestException` on failure instead of returning a tuple.
Updated all consumers to handle exceptions, improving error
handling consistency across the application.
Enhanced error messages for better user feedback and added
logging for improved traceability. Updated `EnvelopeReceiverPage`,
`EnvelopeReceiverPage_DxReportViewer`, and `ReportViewer` to
use the new exception-based API and handle errors gracefully.
This change simplifies the API, improves maintainability, and
makes the application more robust and user-friendly.
