[x] Audit required fields in both admin and student forms
[x] Fix: `checkbox-list.php` partial supports `$required` (fieldset gets `required` + `aria-required`)
[x] Mark `languages` checkbox list as required in both forms
[x] Added visual `*` indicator on all required fields (CSS bold labels + red asterisk)
[x] Added "* Champs obligatoires" note at top of both forms
[x] Verified: all server-side required fields match client-side `required` attrs and visual indicators