Fix TypeScript error in documents page - frontmatter type narrowing

services/web-ui/app/documents/[id]/page.tsx

@@ -71,10 +71,10 @@ export default function DocumentPage() {
           </div>
         )}
 
-        {doc.frontmatter?.summary && (
+        {doc.frontmatter && typeof doc.frontmatter === 'object' && 'summary' in doc.frontmatter && (
           <div className="mb-6 p-4 bg-slate-50 rounded-lg border border-slate-100">
             <p className="text-sm font-medium text-slate-600 mb-1">Summary</p>
-            <p className="text-sm text-slate-700">{doc.frontmatter.summary as string}</p>
+            <p className="text-sm text-slate-700">{String((doc.frontmatter as Record<string, unknown>).summary)}</p>
           </div>
         )}