Task 9: DiscoverTreeAsync UntilStable settle loop (FOCAS) — re-capture on a 1s interval until
the node set is non-empty and stable across two passes, bounded by open-timeout; on
timeout with a prior non-empty capture, return it (best-effort) instead of failing.
Task 11: BrowserSessionService resolves bespoke-first, falls back to IUniversalDriverBrowser
when no bespoke browser matches and CanBrowse is true; new CanBrowse on the service.
16 unit tests green (4 settle + 12 service).
Joseph Doherty
698703744f