Replaced hardcoded German text in the envelope sharing UI and JavaScript alerts with localized resource strings for German, English, and French. Added new translations for labels, prompts, and error/success messages. Improved internationalization and user experience by making the sharing feature fully language-aware.
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.
