fix: harden TTS with 2s await timeout and 4s worker timeout for reliable fallback

Reduces worker generation timeout from 10s to 4s and adds 2s race on
awaitReady so slow Kokoro generation falls back to Web Speech API
quickly instead of stalling the fight.

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

frontend/src/game/tts.ts

@@ -252,7 +252,7 @@ function _workerGenerate(text: string, voice: string, speed: number): Promise<{
     const timeout = setTimeout(() => {
       _pending.delete(id)
       reject(new Error('TTS generation timed out'))
-    }, 10_000)
+    }, 4_000)
     _pending.set(id, {
       resolve: (v) => { clearTimeout(timeout); resolve(v) },
       reject: (e) => { clearTimeout(timeout); reject(e) },
@@ -376,12 +376,15 @@ export function kokoroPrefetch(text: string, profileName: string): void {
   _generateAndCache(text, profileName).catch(() => {})
 }
 
-/** Await until prefetched audio is cached and ready. Returns true if cached, false on failure. */
+/** Await until prefetched audio is cached and ready (max 2s). Returns true if cached, false on timeout/failure. */
 export async function kokoroAwaitReady(text: string, profileName: string): Promise<boolean> {
   if (!_workerReady) return false
   try {
-    const buf = await _generateAndCache(text, profileName)
-    return !!buf
+    const result = await Promise.race([
+      _generateAndCache(text, profileName),
+      new Promise<null>(r => setTimeout(() => r(null), 2000)),
+    ])
+    return !!result
   } catch { return false }
 }