feat: sync TTS voice with chat bubbles and battle log for zero-gap playback

Adds await-then-play pattern: audio is pre-generated and cached before
visuals appear, so log text + speech bubble + mouth animation + voice
all fire in the same frame. Prefetches both answers during question
playback for instant transitions. Adds hideSpeechBubble() to dismiss
bubbles when voice ends instead of fixed 5s timer.

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

frontend/src/game/FightScene.ts

@@ -734,6 +734,19 @@ export async function createFightScene(config: FightSceneConfig) {
     }, duration * 1000)
   }
 
+  function hideSpeechBubble(side: 'a' | 'b') {
+    const els = side === 'a' ? activeBubbleA : activeBubbleB
+    if (!els.length) return
+    els.forEach(el => {
+      if (!el.exists()) return
+      k.tween(el.opacity, 0, 0.25, (v) => { el.opacity = v }).then(() => {
+        if (el.exists()) el.destroy()
+      })
+    })
+    if (side === 'a') activeBubbleA = []
+    else activeBubbleB = []
+  }
+
   function wrapBubbleText(text: string, maxChars: number): string[] {
     const words = text.split(' ')
     const lines: string[] = []
@@ -1195,6 +1208,7 @@ export async function createFightScene(config: FightSceneConfig) {
     showSpeechBubble(side: 'a' | 'b', text: string, duration?: number) {
       showSpeechBubble(side, text, duration)
     },
+    hideSpeechBubble(side: 'a' | 'b') { hideSpeechBubble(side) },
 
     startTalking(side: 'a' | 'b') { startTalking(side) },
     stopTalking(side: 'a' | 'b') { stopTalking(side) },