Every visitor has been on the compiled Dashboard since the 100% rollout, so
the frozen legacy snapshot, its asset route, the per-account selection and
the three TREG_DASHBOARD_ROLLOUT_* settings go. Catalog pages and shared
links no longer look up the session to pick a frontend, /search is always
served, and the app-version stamp is the bundle hash alone. Rollback is now
a deploy of the previous build.