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/lib/devApi.ts

@@ -80,7 +80,7 @@ export type ClientDetailResponse = {
       kty?: string;
       use?: string;
       alg?: string;
-      n?: string;
+      nPreview?: string;
     }>;
   };
 };