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/settings/__tests__/settings.parser.test.ts

@@ -16,6 +16,21 @@ describe('parseSettings()', () => {
       operatorKey: null,
       timeFormat: '24',
       language: 'en',
+      auxTimerNames: ['', '', ''],
     });
   });
+
+  it('carries custom aux timer names through and normalises to a length-3 array', () => {
+    const result = parseSettings({
+      settings: { version: '1', auxTimerNames: ['Speaker'] } as unknown as Settings,
+    });
+    expect(result.auxTimerNames).toStrictEqual(['Speaker', '', '']);
+  });
+
+  it('falls back to defaults when aux timer names are missing or malformed', () => {
+    const result = parseSettings({
+      settings: { version: '1', auxTimerNames: 'not-an-array' } as unknown as Settings,
+    });
+    expect(result.auxTimerNames).toStrictEqual(['', '', '']);
+  });
 });