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/public/partage/language-autre-fragment.php

@@ -18,5 +18,16 @@ $selectedIds  = isset($_POST['languages']) && is_array($_POST['languages'])
     ? $_POST['languages']
     : [];
 $anyChecked   = !empty($selectedIds);
+
+// Also check if any "autre" language pills are present (posted as language_autre[])
+$hasLangAutre = isset($_POST['language_autre']) && is_array($_POST['language_autre'])
+    && count(array_filter($_POST['language_autre'], fn($l) => is_string($l) && trim($l) !== '')) > 0;
+
+// The "Autre(s) langue(s)" label is required if no standard language is checked.
+// The "Langue(s) du TFE" checkbox list is required if neither standard languages
+// nor "autre" languages are set.
+$langAutreRequired = !$anyChecked;
+$checkboxesRequired = !$anyChecked && !$hasLangAutre;
 ?>
-<span id="language-autre-required"><?= !$anyChecked ? ' <span class="asterisk">*</span>' : '' ?></span>
+<span id="language-autre-required"><?= $langAutreRequired ? ' <span class="asterisk">*</span>' : '' ?></span>
+<span id="languages-required-asterisk" hx-swap-oob="true"><?= $checkboxesRequired ? ' <span class="asterisk">*</span>' : '' ?></span>