feat(localization): expand language support and enhance UI for user settings

- Added support for additional UI locales including Cebuano and Spanish, improving accessibility for a broader user base.
- Updated language selection components in the AppHeader and SettingsWidget to reflect new language options, enhancing user experience.
- Enhanced localization of various UI elements across components, ensuring consistent language representation and improved user engagement.
- Implemented logic to synchronize user language preferences with backend settings, providing a seamless experience when changing languages.

frontend/src/i18n/locales/en/personal.json

@@ -2,6 +2,8 @@
     "personal": {
         "calendar": {
             "title": "Calendar",
+            "kicker": "Planning",
+            "intro": "Appointments, birthdays, and your own entries in one structured overview.",
             "today": "Today",
             "newEntry": "New Entry",
             "editEntry": "Edit Entry",