fix(headless-login): show parsed jwks n preview

- reproduce the missing n preview with the actual parsedKeys response shape
- read nPreview from DevFront instead of the old n field
- keep the preview text as provided by backend summaries

devfront/src/features/clients/ClientGeneralPage.tsx

@@ -102,12 +102,6 @@ function formatDateTime(value?: string) {
   return date.toLocaleString();
 }
 
-function previewKeyMaterial(value?: string) {
-  if (!value) return "-";
-  if (value.length <= 23) return value;
-  return `${value.slice(0, 10)}...${value.slice(-10)}`;
-}
-
 function ClientGeneralPage() {
   const params = useParams();
   const navigate = useNavigate();
@@ -1347,7 +1341,7 @@ function ClientGeneralPage() {
                                   )}
                                 </p>
                                 <p className="break-all rounded-lg border border-border bg-background px-3 py-2 font-mono text-[11px]">
-                                  {previewKeyMaterial(key.n)}
+                                  {key.nPreview || "-"}
                                 </p>
                               </div>
                             </div>