fix(timer): address review findings on the group timer

- keep the pending and none phases when showing the group timer. These describe the
  playback state rather than a threshold, so collapsing them made roll standby render
  as a running countdown and silently dropped user styling keyed on the phase
- only show the group indicator for timer types which render the running timer. It was
  labelling the wall clock, and the invisible display of the none timer type, as a group
- accept useGroupTimer in the MCP group patch. It was documented in the group shape but
  dropped on write, which reported success without applying the change
- narrow the timer preview tooltip, which claimed all views follow the group timer when
  only the timer views do

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Kniqs443KUNCRABwVJwT7K

apps/client/src/features/control/message/TimerPreview.tsx

@@ -107,7 +107,7 @@ export default function TimerPreview() {
           <LuArrowDownToLine />
         </Tooltip>
         <Tooltip
-          text={isGroupTimerActive ? 'Views are showing the shared group timer' : 'Views are showing the event timer'}
+          text={`Timer views are showing the ${isGroupTimerActive ? 'shared group timer' : 'event timer'}`}
           render={<span />}
           className={style.statusIcon}
           data-active={isGroupTimerActive}