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

packages/types/src/definitions/core/Settings.type.ts

@@ -6,4 +6,6 @@ export type Settings = {
   operatorKey: null | string;
   timeFormat: TimeFormat;
   language: string;
+  /** Custom names for the aux timers, indexed by aux timer (1, 2, 3). Empty string falls back to the default label */
+  auxTimerNames: string[];
 };