feat(voice): play TTS through tablet speakers via ElevenLabs proxy

Stage 2 of voice integration — centralizes TTS on the tablet so the
Python satellite no longer needs ElevenLabs credentials or mpv.

- app/api/voice/tts — POST {text, agent}, proxies to ElevenLabs
  streaming endpoint with flash_v2_5 default, returns audio/mpeg.
  Per-agent voice id via COSMO_TTS_VOICE / LUSYA_TTS_VOICE env.
- VoiceOverlay — on response/error events fetches TTS and plays via
  HTMLAudioElement; on wake event stops playback (barge-in). Dismiss
  timer extended by text length so long responses do not cut off.
- Autoplay caveat: browser may block first playback until user taps
  anywhere on the page (FKB: enable Force Autoplay to bypass).

components/VoiceOverlay.tsx

@@ -34,6 +34,55 @@ export default function VoiceOverlay() {
     dismissTimer.current = setTimeout(() => setState('idle'), ms)
   }
 
+  const audioRef = useRef<HTMLAudioElement | null>(null)
+  const audioUrlRef = useRef<string | null>(null)
+
+  const stopAudio = () => {
+    if (audioRef.current) {
+      try {
+        audioRef.current.pause()
+        audioRef.current.src = ''
+      } catch {}
+      audioRef.current = null
+    }
+    if (audioUrlRef.current) {
+      URL.revokeObjectURL(audioUrlRef.current)
+      audioUrlRef.current = null
+    }
+  }
+
+  const playTTS = async (textToSpeak: string, agentId: Agent) => {
+    stopAudio()
+    if (!textToSpeak) return
+    try {
+      const r = await fetch('/api/voice/tts', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ text: textToSpeak, agent: agentId }),
+      })
+      if (!r.ok) {
+        console.warn('TTS endpoint error:', r.status)
+        return
+      }
+      const blob = await r.blob()
+      const url = URL.createObjectURL(blob)
+      audioUrlRef.current = url
+      const audio = new Audio(url)
+      audio.onended = () => {
+        if (audioUrlRef.current === url) {
+          URL.revokeObjectURL(url)
+          audioUrlRef.current = null
+        }
+      }
+      audioRef.current = audio
+      await audio.play().catch(err => {
+        console.warn('Audio autoplay blocked:', err)
+      })
+    } catch (err) {
+      console.warn('TTS fetch failed:', err)
+    }
+  }
+
   useEffect(() => {
     let es: EventSource | null = null
     let retry: ReturnType<typeof setTimeout> | null = null
@@ -45,12 +94,15 @@ export default function VoiceOverlay() {
       es.onmessage = (e) => {
         try {
           const evt: VoiceEvent = JSON.parse(e.data)
+          const currentAgent: Agent = evt.agent ?? agent
           if (evt.agent) setAgent(evt.agent)
 
           if (evt.event === 'wake') {
+            // Barge-in: cut any ongoing TTS when user speaks again
+            stopAudio()
             setState('wake')
             setText('')
-            scheduleDismiss(20000) // safety net: 20s max without command
+            scheduleDismiss(20000)
           } else if (evt.event === 'command') {
             setState('command')
             setText(evt.text || '')
@@ -58,11 +110,13 @@ export default function VoiceOverlay() {
           } else if (evt.event === 'response') {
             setState('response')
             setText(evt.text || '')
-            scheduleDismiss(6000)
+            if (evt.text) playTTS(evt.text, currentAgent)
+            scheduleDismiss(Math.max(6000, (evt.text?.length || 0) * 80))
           } else if (evt.event === 'error') {
             setState('error')
             setText(evt.text || 'Ошибка')
-            scheduleDismiss(4000)
+            if (evt.text) playTTS(evt.text, currentAgent)
+            scheduleDismiss(5000)
           } else if (evt.event === 'idle') {
             clearDismiss()
             setState('idle')
@@ -82,9 +136,12 @@ export default function VoiceOverlay() {
     return () => {
       closedByUs = true
       clearDismiss()
+      stopAudio()
       if (retry) clearTimeout(retry)
       es?.close()
     }
+    // agent is intentionally omitted — we always read from ref via the evt
+    // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [])
 
   const isActive = state !== 'idle'