feat: allow naming aux timers

Adds custom, persisted names for the three aux timers, editable in the
editor settings and surfaced everywhere an aux title is shown.

- Persist `auxTimerNames` on the Settings object (default empty, falls
  back to the stock "Aux N" label when unset). Reuses the existing
  settings pipeline: validation sanitises to a fixed-length trimmed
  array, the parser normalises loaded/legacy data, and migrations carry
  the field forward.
- New "Aux timers" settings section to name each timer, plus a shortcut
  button next to the aux timers in the playback control that jumps
  straight to it.
- Resolve names via a shared getAuxTimerLabel helper in the aux timer
  control, Studio view, secondary-source selector and preview, and the
  automation action labels.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WCZejVTzuAY3tHTE6nB3JH

apps/client/src/views/studio/Studio.tsx

@@ -49,7 +49,7 @@ function Studio({ customFields, projectData, isMirrored, settings, viewSettings
 
       <div className={cx(['studio-contents', hideCards && 'studio-contents--onecol'])}>
         <StudioClock hideCards={hideCards} />
-        {!hideCards && <StudioTimers viewSettings={viewSettings} />}
+        {!hideCards && <StudioTimers viewSettings={viewSettings} auxTimerNames={settings?.auxTimerNames} />}
       </div>
     </div>
   );