fix: prevent memory leaks on consecutive fight replays

- FightViewer: store canvas event handlers and remove them before
  replacing canvas elements, preventing detached DOM/closure leaks
- FightViewer: clean up canvas listeners on unmount
- tts.ts: clear _staticLoading dedup map after precache completes

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

frontend/src/game/tts.ts

@@ -358,6 +358,8 @@ async function _precacheCommon() {
   }
   _precacheDone = true
   _precacheRunning = false
+  // Release dedup promises — they hold closures referencing fetch/decode state
+  _staticLoading.clear()
 }
 
 function _cacheKey(text: string, profile: string): string {