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/server/src/api-data/db/migration/db.migration.v3.ts

@@ -74,7 +74,7 @@ export function migrateSettings(jsonData: object): (Settings & { serverPort: num
     const { serverPort, editorKey, operatorKey, timeFormat, language } = structuredClone(
       jsonData.settings,
     ) as old_Settings;
-    return { version: '4.0.0', serverPort, editorKey, operatorKey, timeFormat, language };
+    return { version: '4.0.0', serverPort, editorKey, operatorKey, timeFormat, language, auxTimerNames: ['', '', ''] };
   }
 }