fix(oxauth): add waitForPageSwitch to wait for last redirect

After clicking the consent-page Allow button, HtmlUnit follows the redirect chain (JSF postback -> restv1/authorize -> final device_authorization.htm?code=...) in a background JS thread, but waitForPageSwitch returns on the first URL change

Start by locating the oxauth implementation and tests for waitForPageSwitch, then trace the consent-page Allow flow through the listed redirect chain. Confirm the wait does not return until the final device_authorization.htm?code=... URL is reached, and add or update coverage for that behavior.

Written by the indexing model from the issue text.