refactor: split sounds.ts into audio/ modules

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

frontend/src/pages/SoundboardPage.vue

@@ -1,7 +1,7 @@
 <script setup lang="ts">
 import { ref, computed, onMounted } from 'vue'
 import { getVoiceMap, isKokoroReady, isKokoroLoading } from '../game/tts'
-import { speak, ensureAudioContext } from '../game/sounds'
+import { speak, ensureAudioContext } from '../game/audio'
 
 const voiceMap = getVoiceMap()
 const allProfiles = Object.entries(voiceMap).map(([name, { voice, speed }]) => ({