fix: mobile menu overlay, speech bubble timing, TTS static file fallback

- Mobile nav menu now overlays content (absolute positioning) instead of
  pushing it down
- Speech bubbles stay visible for minimum 400ms even when TTS resolves
  instantly or fails
- kokoroPlayCached checks audio cache and loads static files even when
  Kokoro worker hasn't loaded — fixes TTS not playing on production
- CORS_ORIGIN env now supports comma-separated origins
- Rename "VIDEO REPLAY" to play icon + "REPLAY"

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

frontend/src/components/FightViewer.vue

@@ -441,8 +441,11 @@ async function _doReplay() {
         scene.showSpeechBubble('a', round.botAResponse.slice(0, 60), 8)
         scene.startTalking('a')
       }
+      // Ensure bubble stays visible for at least 400ms even if TTS resolves instantly
+      const minBubbleA = sleep(400).catch(() => {})
       if (doTTS) await playAnswerNow(props.fight.botA!.name, round.botAResponse)
-      else await sleep(insanityMode.value ? 30 : 400)
+      await minBubbleA
+      if (!doTTS && !insanityMode.value) await sleep(400)
       scene?.stopTalking('a')
       scene?.hideSpeechBubble('a')
     }
@@ -460,8 +463,10 @@ async function _doReplay() {
         scene.showSpeechBubble('b', round.botBResponse.slice(0, 60), 8)
         scene.startTalking('b')
       }
+      const minBubbleB = sleep(400).catch(() => {})
       if (doTTS) await playAnswerNow(props.fight.botB!.name, round.botBResponse)
-      else await sleep(insanityMode.value ? 30 : 400)
+      await minBubbleB
+      if (!doTTS && !insanityMode.value) await sleep(400)
       scene?.stopTalking('b')
       scene?.hideSpeechBubble('b')
     }
@@ -809,7 +814,11 @@ async function _doReplay() {
           :disabled="isReplaying"
           @click="replay"
         >
-          {{ isReplaying ? 'FIGHTING...' : 'VIDEO REPLAY' }}
+          <span v-if="isReplaying">FIGHTING...</span>
+          <span v-else class="flex items-center gap-1.5">
+            <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="currentColor" class="w-3.5 h-3.5"><path d="M8 5v14l11-7z"/></svg>
+            REPLAY
+          </span>
         </button>
         <button
           class="w-8 h-8 flex items-center justify-center border border-border/50 text-text-muted

frontend/src/components/NavBar.vue

@@ -85,7 +85,7 @@ const bottomNav = [
       </button>
     </div>
 
-    <div v-if="isMenuOpen" class="md:hidden border-t border-border px-6 py-4 space-y-4 bg-surface">
+    <div v-if="isMenuOpen" class="md:hidden absolute left-0 right-0 top-full border-t border-border px-6 py-4 space-y-4 bg-surface/95 backdrop-blur-md z-50">
       <RouterLink
         v-for="link in links"
         :key="link.to"