Removed fixed column widths in `EnvelopeSenderPage.razor` for dynamic sizing. Added `CellDisplayTemplate` to `Title`, `Status`, and `EnvelopeReceivers` columns for custom data rendering. Fixed gradient typo in progress bar CSS.
Added a new CSS rule to hide empty DevExpress grid cells and updated `sender-page.css` to include this rule while preserving existing styles.
Moved inline styles from `EnvelopeSenderPage.razor` to a new
`sender-page.css` file for better maintainability and separation
of concerns. Updated `EnvelopeSenderPage.razor` to use versioned
URLs for stylesheets via the newly injected `AppVersionService`,
enabling cache-busting. Added responsive design support in
`sender-page.css` to improve layout on smaller screens.
