Timer ready-check list shows participants from all rooms in breakout rooms

The timer module's ready-check participant list shows every joined participant in the conference, even when the user is inside a breakout room. It should only list participants of the active room/breakout room.

Root cause: selectParticipantsReadyList in app/src/store/selectors.ts was derived from selectAllOnlineParticipantsInConference (unscoped, whole conference) instead of selectAllOnlineParticipants, which filters by currentBreakoutRoomId (app/src/store/slices/participantsSlice.ts).

Fix: build selectParticipantsReadyList from selectAllOnlineParticipants.