The audit signs in as a guest per device, which creates a real account. A single
long-lived browser was crashing partway through the third device, and the crash
took the teardown with it — leaving throwaway accounts in production.

Now: one browser per device, and teardown in a finally block so it runs whichever
way the run ends.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>