Extend TalkSDK and AudioClient with Lemonade ASR+TTS auto-detection

[kovtcharov]

Summary

Wire the new LemonadeASR (#372) and LemonadeTTS (#373) backends into the existing TalkSDK and AudioClient so that gaia talk seamlessly uses Lemonade server-side audio when available, with graceful fallback to local Whisper/Kokoro.

Current State

• AudioClient (src/gaia/audio/audio_client.py) hardcodes local WhisperAsr and KokoroTTS
• TalkSDK (src/gaia/talk/sdk.py) has no backend selection mechanism
• TalkConfig has whisper_model_size but no asr_backend / tts_backend fields

Changes Required

File	Change	Effort
src/gaia/talk/sdk.py	Add asr_backend: str = "auto" and tts_backend: str = "auto" to TalkConfig. "auto" checks Lemonade first, falls back to local. Also accepts "lemonade" or "local".	Medium
src/gaia/audio/audio_client.py	Add auto-detection logic: check Lemonade /health for websocket_port → if present, use LemonadeASR; check loaded models for kokoro-v1 → if present, use LemonadeTTS. Log which backend is active.	Medium
src/gaia/cli.py	Add --asr-backend and --tts-backend flags to gaia talk command	Low
tests/unit/test_audio_backend_selection.py	Test auto-detection logic with mocked health responses	Medium
tests/integration/test_talk_lemonade.py	End-to-end test with real Lemonade server	Medium

Auto-Detection Logic

def _select_asr_backend(self):
    if self.config.asr_backend == "local":
        return WhisperAsr(...)
    # Try Lemonade first
    try:
        ws_port = self.lemonade_client.get_websocket_port()
        if ws_port:
            logger.info("Using Lemonade server-side ASR (Whisper.cpp)")
            return LemonadeASR(ws_port=ws_port, ...)
    except Exception:
        pass
    # Fallback
    logger.info("Using local Whisper ASR")
    return WhisperAsr(...)

Dependencies

• Add streaming transcription via Lemonade WebSocket realtime API #372 (streaming ASR — creates LemonadeASR class)
• Add server-side TTS via Lemonade audio/speech endpoint #373 (server-side TTS — creates LemonadeTTS class)
• Add websockets to talk extras and update dependency groups #382 (websockets dependency)

Acceptance Criteria

• gaia talk auto-detects and uses Lemonade ASR/TTS when server is running
• Falls back to local Whisper/Kokoro when Lemonade is unavailable
• --asr-backend and --tts-backend CLI flags override auto-detection
• Backend selection logged clearly at startup
• Existing gaia talk behavior unchanged when Lemonade is not running
• Latency improvement measurable when using Lemonade backend