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

app/templates/partials/form/language-search.php

@@ -100,6 +100,14 @@ $langCount      = count($selectedLanguages);
         if (countEl) countEl.textContent = n + '/' + maxLanguages;
         if (counter) counter.style.display = (n > 0) ? '' : 'none';
 
+        // Toggle the checkbox-list asterisk: if any "autre" language pill
+        // is present, the checkbox list is no longer required.
+        const asteriskEl = document.getElementById('languages-required-asterisk');
+        if (asteriskEl) {
+            const checkboxes = document.querySelectorAll('#languages-fieldset input[type="checkbox"]:checked');
+            asteriskEl.innerHTML = (n === 0 && checkboxes.length === 0) ? ' <span class="asterisk">*</span>' : '';
+        }
+
         // Show/hide search input based on max
         const wrap = container.querySelector('.tag-search-input-wrap');
         const maxMsg = container.querySelector('.tag-search-max-msg');