When enabled, each workgroup collapses to a single row whose
representative is the highest-priority status, with ties broken by
the most recent update. Solo sessions remain individual rows. When
disabled, the prior per-session behavior is preserved.

The Session Status model is now split into the full per-session
list and a table-facing displayedStatuses that the merge rebuilds.
Selecting the active session also maps through the workgroup so the
merged row highlights when any peer is focused.