fix: replace raw setTimeout with tracked timers in game audio (BUG-4)

Added audioTimeout() to audio/context.ts — tracked timer set cleared on
scene destroy via clearAllAudioTimers(). Converted 20 sfx.ts + 3 voice.ts
raw setTimeout calls to audioTimeout. Converted FightScene playEntrance
timeout to trackedTimeout. Remaining setTimeout in tts.ts worker layer
and music.ts (already tracked via setMusicTimeout) are self-managing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/game/FightScene.ts

@@ -32,7 +32,7 @@ import {
   sfxJetpack, sfxExplosion, sfxBlock, sfxDodge, sfxClash, sfxRandomSilly,
   sfxBoing, sfxBonk, sfxZap, sfxSlideDown, sfxSlideUp, sfxZoomWhoosh,
   sfxRapidPunch, sfxPowerUp, sfxCoin, sfxRandomComedy,
-  startMusic, stopMusic, announceCool,
+  startMusic, stopMusic, announceCool, clearAllAudioTimers,
 } from './audio'
 
 
@@ -1225,7 +1225,7 @@ export async function createFightScene(config: FightSceneConfig) {
       // Timeout entrance to prevent hanging on mobile (max 8s)
       await Promise.race([
         entranceSystem.playEntrance(),
-        new Promise<void>(r => setTimeout(r, 8000)),
+        new Promise<void>(r => trackedTimeout(r, 8000)),
       ])
     },
 
@@ -1285,6 +1285,8 @@ export async function createFightScene(config: FightSceneConfig) {
         clearTimeout(id)
       }
       cleanupTimers.clear()
+      // Clear audio timers (SFX/voice stagger delays)
+      clearAllAudioTimers()
       // Destroy all remaining game objects before quitting
       try { k.get('*').forEach(o => { if (o.exists()) o.destroy() }) } catch {}
       k.quit()