feat: SSE live fight spectating with spectator count

Enable real-time fight spectating for all live fights (not just human
fights). Multiple spectators can watch simultaneously via SSE. Spectator
count is tracked per-fight and broadcast with every SSE event.

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

frontend/vite.config.ts

@@ -55,8 +55,23 @@ export default defineConfig({
       },
     }),
   ],
+  worker: {
+    format: 'es', // Required for dynamic import('kokoro-js') inside the TTS worker
+  },
+  optimizeDeps: {
+    // Pre-bundle kokoro-js on first startup so Vite doesn't stall mid-page-load
+    // discovering it as a new dep. The 4.8MB bundle is cached in node_modules/.vite/deps.
+    include: ['kokoro-js'],
+  },
   server: {
     port: 9101,
+    headers: {
+      // Enable SharedArrayBuffer for onnxruntime WASM threads.
+      // Without these, Kokoro TTS runs single-threaded on the main thread,
+      // blocking the UI for seconds on every TTS generation.
+      'Cross-Origin-Opener-Policy': 'same-origin',
+      'Cross-Origin-Embedder-Policy': 'credentialless',
+    },
     proxy: {
       '/api': {
         target: 'http://localhost:9100',