Switching to a profile whose only server is offline verified the PIN,
failed the bind with zero reachable servers, and rolled back to the
previous profile — whose scope owns none of the downloads. The Downloads
UI then showed nothing while the files and pinned metadata sat intact on
disk. Startup offline mode only covered the cold-start bind, so such a
profile could never be entered while its server was away.
The binder now classifies a settled bind failure as connectivity-only
when the profile expected servers, reached none, and none were
auth-rejected (snapshotting auth markers before the visibility sweep,
which clears them via removeServer). On such a failure,
switchProfileFromUi keeps the profile active when it owns downloads
instead of rolling back; OfflineModeProvider drives the offline UI from
the empty visible-server set. Auth failures, PIN cancels, and
downloads-free profiles keep the existing rollback and error snackbar.
close#1927