Fix: Cast iframe ref to any for React 19 compat

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

website/app/admin/content/_components/LivePreviewPanel.tsx

@@ -42,7 +42,7 @@ export default function LivePreviewPanel({ activeTab, iframeRef }: LivePreviewPa
       {/* Preview Frame */}
       <div className="relative h-[calc(100vh-340px)] bg-slate-100">
         <iframe
-          ref={iframeRef}
+          ref={iframeRef as any}
           src={`/?preview=true&section=${activeTab}#${activeTab}`}
           className="w-full h-full border-0 scale-75 origin-top-left"
           style={{