feat: require 3 mots-clés in partage, language asterisk toggle, admin auto-save checkboxes

- tag-search: add minTags/required params, counter shows red if < 3, accent if ≥ 3
- form.php: pass minTags=3 for partage mode keywords
- checkbox-list: support labelHtml for raw HTML label with targetable asterisk span
- language-autre-fragment: OOB swap updates #languages-required-asterisk when autre pills change
- language-search: client-side update #languages-required-asterisk on pill add/remove
- contenus.php: replace 3 form+submit-button fieldsets with HTMX auto-save checkboxes
- settings.php: detect HX-Request header, return OOB CSRF token updates, skip redirect

TODO.md

@@ -3,6 +3,9 @@
 - [x] Fix email addresses in about.php contacts section not using EmailObfuscator for link text
 - [x] Raise rate limits: SearchController 30→300, request-access 3→30, partage 5→50
 - [x] Make Libre option toggleable in Degré d'ouverture fieldset, move to top, remove temporary note
+- [x] Mots-clés required (min 3) in partage form: red count < 3, accent ≥ 3
+- [x] Language checkbox-list no longer required when language_autre pill is present
+- [x] Admin contenus: auto-save checkboxes via HTMX (Restrictions, Degré d'ouverture, Types de travaux), remove Enregistrer buttons
 - [x] Improve recapitulatif.php (partage): bottom margin/padding, center .thanks-success
 - [x] Display ALL submitted info in recapitulatif page + email recap
 - [x] Add "validate your info / contact xamxam@erg.be" note on recap page