feat: replace Web Speech API with Kokoro TTS for high-quality voices

Adds kokoro-js (82M model, 28 distinct voices) as primary TTS engine with
automatic fallback to speechSynthesis while model loads. All 60+ voice
profiles mapped to real Kokoro voices. Common fight phrases pre-cached
for instant playback.

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

frontend/package.json

@@ -9,6 +9,7 @@
   },
   "dependencies": {
     "kaplay": "^3001.0.19",
+    "kokoro-js": "^1.2.1",
     "nostr-tools": "^2.23.3",
     "vue": "^3.5.13",
     "vue-router": "^4.5.1"