REST additions: GET /topology returns mode (hidden/public/unknown) + sender/receiver group lists. POST /topology/apply confines local senders to teamsiso-input + receivers to public+teamsiso-input. POST /topology/restore returns both to public defaults.
GET /participants/{id}/thumbnail.jpg encodes the latest engine ProcessedFrame as a 192-wide JPEG. 404 when no pipeline is running. Used by the /ui control panel for live preview tiles.
Settings: ControlSurfaceEnabled now persists across sessions via UIPreferences and auto-starts the server on app launch when previously enabled.
/ui control panel rebuilt: live thumbnail per row, topology toggle card with Hide/Restore buttons, removed dead recording marker button, larger layout (920px), participant rows in single card with hover affordances.
