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/checkbox-list.php

@@ -9,7 +9,8 @@
  *
  * Variables consumed:
  *   string  $name      — input name attribute (will be posted as array: name[])
- *   string  $label     — group label text
+ *   string  $label     — group label text (htmlspecialchars'd unless $labelHtml is set)
+ *   string  $labelHtml — raw HTML label override (bypasses htmlspecialchars, optional)
  *   array   $options   — each element must have 'id' and 'name' keys
  *   array   $checked   — array of 'id' values that are currently checked
  *   bool    $required  — whether at least one checkbox must be checked; default false
@@ -27,7 +28,7 @@ $hxSwap     = $hxSwap     ?? 'outerHTML';
 $hxInclude  = $hxInclude  ?? 'this';
 ?>
 <div>
-    <span class="admin-row-label"><?= htmlspecialchars($label) ?><?= $required ? ' <span class="asterisk">*</span>' : '' ?></span>
+    <span class="admin-row-label"><?= isset($labelHtml) ? $labelHtml : (htmlspecialchars($label) . ($required ? ' <span class="asterisk">*</span>' : '')) ?></span>
     <fieldset class="admin-checkbox-group"
               <?= $required ? ' required aria-required="true"' : '' ?>
               <?php if ($hxPost !== ''): ?>