feat: render actual elements in markdown cheatsheet instead of labels

Replace text labels (h1, bold, italic) with rendered HTML in the Rendu column:
headings, strong, em, del, code, links, blockquote, lists, hr, sup, small

app/templates/admin/apropos-groups-form.php

@@ -6,7 +6,11 @@
  *   $groups      array   Existing groups data
  */
 ?>
-<form action="/admin/actions/apropos.php" method="post" class="admin-form" id="apropos-form-<?= $aproposKey ?>" data-autosave>
+<form action="/admin/actions/apropos.php" method="post" class="admin-form" id="apropos-form-<?= $aproposKey ?>"
+      hx-post="/admin/actions/apropos.php"
+      hx-trigger="change delay:1500ms, input delay:1500ms"
+      hx-swap="none"
+      hx-on::after-request="handleAutosaveResponse(event)">
     <input type="hidden" name="csrf_token" value="<?= htmlspecialchars($_SESSION['csrf_token']) ?>">
     <input type="hidden" name="apropos_key" value="<?= htmlspecialchars($aproposKey) ?>">