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/src/App.tsx

@@ -39,7 +39,6 @@ const App: React.FC<{ children: React.ReactNode }> = ({ children }) => {
     <Suspense fallback={<SuspenseFallback />}>
       <ThemeWrapper>
         <RouterProvider router={router} future={{ v7_startTransition: true }} />
-        <PreferenceSelector />
       </ThemeWrapper>
     </Suspense>
   );