Introduced a "Send Confirmation" popup to improve user experience
when sending envelopes. The popup allows users to review recipients,
signature fields, and settings before confirming the send action.
- Added localized strings in `Resource.de-DE.resx`, `Resource.en-US.resx`,
and `Resource.fr-FR.resx` for confirmation messages and actions.
- Updated `SenderEditorPage.razor` to include the confirmation popup
(`DxPopup`) with body and footer templates.
- Added `RequestSendAsync` and `ConfirmSendAsync` methods to manage
the confirmation process and sending logic.
- Replaced the old success popup logic with direct navigation to the
sender dashboard after a successful send.
- Updated the toolbar button to trigger the confirmation popup.
- Styled the confirmation popup in `envelope-viewer.css`, including
support for dark themes.
- Ensured proper state management for the popup and sending process.
These changes enhance usability by providing a clear confirmation
step and progress feedback during envelope sending.