feat: redesign language switcher as dropdown, add cursor pointers

Replace flag-row selector with a dropdown to fix distorted flag icons
and remove the colored ring border. Add cursor-pointer to the language
menu and download submit button.

src/components/SubmitForm.tsx

@@ -81,7 +81,7 @@ export function SubmitForm() {
           <button
             type="submit"
             disabled={loading}
-            className="flex items-center gap-2 px-5 py-3 bg-violet-600 hover:bg-violet-700 dark:bg-violet-500 dark:hover:bg-violet-600 text-white text-sm font-medium transition-colors disabled:opacity-60"
+            className="flex items-center gap-2 px-5 py-3 bg-violet-600 hover:bg-violet-700 dark:bg-violet-500 dark:hover:bg-violet-600 text-white text-sm font-medium transition-colors disabled:opacity-60 cursor-pointer disabled:cursor-not-allowed"
           >
             {loading && <Spinner />}
             {loading ? t('submitting') : t('submit')}