Completes full internationalization coverage for the webmail application with enhanced language support:
- Replace all remaining hardcoded English strings with translation keys
- Add timezone auto-detection to prevent hydration mismatches
- Enable instant client-side language switching without page reload
- Add 60+ new translation keys in English and French locales
- Improve language switcher component with proper state management
- Add health check endpoint for container orchestration
All user-facing text now supports English and French with no hardcoded fallbacks, providing a fully localized experience.
