Introduced a new `AccessCode` property in `EnvelopeReceiverDto` to support displaying and copying access codes in the envelope sender page.
- Updated `EnvelopeReceiverDto` to include the nullable `AccessCode` property.
- Enhanced `EnvelopeSenderPage.razor` to display the `AccessCode` for each receiver, with a copy-to-clipboard button.
- Implemented `CopyAccessCodeAsync` for clipboard functionality using JavaScript interop.
- Styled the `AccessCode` section in `sender-page.css` for a responsive and user-friendly design.
- Improved error handling for clipboard operations with console warnings.
These changes improve the user experience by allowing senders to view and copy access codes for receivers.
Added a `Histories` property to `EnvelopeDto` to track envelope
history entries for actions like `DocumentSigned` and
`EnvelopeOpened`. Introduced a computed `Signed` property in
`EnvelopeReceiverDto` to determine if a receiver has signed the
envelope based on the history. Updated `using` directives to
support these changes.
