Added "DocumentSharingPeriodExpired" and "Expired" keys to de-DE, en-US, and fr-FR resource files. Updated EnvelopeExpired.cshtml to use localized strings for the title, heading, and message, enabling full internationalization of the expired envelope page.
Refactored Culture model to use required and non-nullable properties.
Removed nullable checks for Info in ShowEnvelope.cshtml.
Changed DI from Cultures to MultiCulture in _ViewImports.cshtml.
A "Refresh" button with a counterclockwise arrow icon is now shown in the envelope UI, but only when the envelope is not in read-only mode. The button uses standard styling classes for consistency.
