feat(settings): add appearance settings with dark mode toggle and translations

- Introduced new appearance settings page with a dark mode toggle feature.
- Added localization support for English, Spanish, and Portuguese in appearance settings.
- Removed the ThemeSelector component and updated PreferenceSelector accordingly.

worklenz-frontend/public/locales/es/settings/appearance.json

@@ -0,0 +1,5 @@
+{
+  "title": "Apariencia",
+  "darkMode": "Modo Oscuro",
+  "darkModeDescription": "Cambia entre el modo claro y oscuro para personalizar tu experiencia visual."
+}