fix(headless-login): show full parsed jwks key values

- return the full RSA n value in parsedKeys responses
- render parsed key fields with labels and multiline key material in DevFront
- lock the behavior with backend and Playwright regression tests

devfront/tests/helpers/devfront-fixtures.ts

@@ -33,7 +33,7 @@ export type Client = {
       kty?: string;
       use?: string;
       alg?: string;
-      nPreview?: string;
+      n?: string;
     }>;
   };
   metadata?: Record<string, unknown>;