BrowserSession wraps headless Chrome via thirtyfour. Auth helper injects
session cookies to bypass WebAuthn. Wait helpers handle Datastar's async
DOM updates (visibility, text, URL). Form helpers find visible elements
to avoid hidden duplicates on tabbed pages. Chromedriver is auto-spawned
on first use via a dedicated parked thread with PR_SET_PDEATHSIG so the
kernel kills it when the test binary exits.
