Sounds settings panel (enable/test, volume, mute, start-tone config, future callouts)

[ryan-johnson2]

Sounds settings panel (deferred)

A dedicated place to configure audio, replacing the removed inline test-tone button. All audio plays through the console (browser now, Tauri webview later) — see docs/decisions.html / the start-tone work.

• Enable / Test tone: a definite user gesture to unlock the AudioContext and play a confirmation beep (prime + verify audio + PA before a race).
• Volume + Mute: master audio level and a global mute (the per-event mute toggle exists today).
• Start-procedure tone config: per-event tone choice / pattern for the race-go cue (today it's a fixed 880Hz square on entering Running).
• Channel callouts (future): announce laps by channel/pilot (Web Audio tones and/or TTS) — the larger feature this panel sets up.

Context: the start tone fires on a genuine race-go (suppressed on navigation); this panel is its proper configuration home.