alter table public.student_profiles
  add column if not exists avatar_preset text not null default 'male';

alter table public.student_profiles
  drop constraint if exists student_profiles_avatar_preset_check,
  add constraint student_profiles_avatar_preset_check
    check (avatar_preset in ('male', 'female'));

comment on column public.student_profiles.avatar_preset is
  'Student profile preset avatar choice. User-uploaded avatars are intentionally unsupported.';