- Added CSS styles for `.pdf-viewer` and its child elements
to ensure proper dimensions and layout for PDF display.
- Enhanced `EnvelopeReceiverPage_DxPdfViewer.razor` with
conditional rendering for improved user feedback.
- Introduced `EnvelopeReceiverPage_embed.razor` with a new
route `/envelope/Embed`, drag-and-drop file upload, and
embedded PDF viewer using `<embed>`.
- Implemented default PDF loading from embedded resources
and Base64 encoding for embedding.
- Refactored file upload handling with `OnFilesUploading`
and centralized allowed file types logic.
- Improved user experience with success and informational
messages for file upload and PDF viewing.