RoomNavCategoryButton set open/closed only through its chevron. It now sets
aria-expanded from `closed` (absent when the section does not toggle); tested by
rendering to static markup.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
A steward group with no joined or invited room collapses into "Browse N more rooms"
per tier, closed on every screen and remembered per device; a group the user is in
anything of, loose estate rooms, and joined rooms stay up front. splitGroups is the
pure rule, tested.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>