fix: Markdown import in admin preview route

src/volumen/admin_routes.py

@@ -316,11 +316,11 @@ async def admin_preview(
     """Render Markdown body to HTML and return it."""
     await validate_csrf_form(request)
 
-    from .markdown import Markdown
+    from .markdown import render
 
     form = await request.form()
     body = str(form.get("body", ""))
-    html = Markdown.render(body)
+    html = render(body)
     return HTMLResponse(content=html)