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/footer.php

@@ -7,6 +7,9 @@
        hx-target="#toast-region">
 </aside>
 
+<!-- Markdown cheatsheet container (filled by HTMX on demand) -->
+<div id="md-cheatsheet-container"></div>
+
 <?php foreach ($extraJs ?? [] as $js): ?>
 <script src="<?= App::assetV($js) ?>"></script>
 <?php endforeach; ?>
@@ -30,6 +33,19 @@ document.body.addEventListener('htmx:afterSettle', function (e) {
         if (warn) { warn.setAttribute('tabindex', '-1'); warn.focus(); }
     }
 });
+
+// Markdown cheatsheet: close on backdrop click, remove stale dialogs before new one arrives
+document.body.addEventListener('htmx:beforeRequest', function(e) {
+    if (e.detail.requestConfig && e.detail.requestConfig.path === '/admin/markdown-cheatsheet-fragment.php') {
+        var old = document.getElementById('md-cheatsheet-dialog');
+        if (old) old.remove();
+    }
+});
+document.body.addEventListener('click', function(e) {
+    if (e.target.tagName === 'DIALOG' && e.target.id === 'md-cheatsheet-dialog') {
+        e.target.close();
+    }
+});
 </script>
 </body>
 </html>