Moved inline styles from `EnvelopeViewer.razor` to a new external
CSS file `envelope-viewer.css` for better maintainability and
separation of concerns. Added external JavaScript dependencies
(`pdf.js` and `pdf-viewer.js`) to enable PDF rendering.
Fixed encoding issues in error messages and improved the layout
structure with responsive design rules. Enhanced readability and
usability by organizing styles and ensuring proper localization
support.
TekH
f1ebd47c77