feat(audio): passing tone only during races and remove legacy audio

Adds 'Calls during a race' (default: passing tone only, like timing
systems) that drops name/personal best/leader/position calls in race
sessions; practice keeps them. Removes the legacy audio panel and
fallbacks, including its 'Sound on' switch that silently muted every
race-audio voice.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "rc-racecore",
-  "version": "1.27.0",
+  "version": "1.28.0",
   "private": true,
   "description": "RC RaceCore live timing and race control with AMMC ingest and SQLite persistence",
   "engines": {