Add support for Xfyun ASR and TTS services in the backend

- Introduce new Xfyun ASR and TTS services, enabling integration with iFlytek's voice recognition and synthesis capabilities.
- Update AssistantConfig model to include interface types for STT and TTS.
- Enhance credential testing to validate Xfyun credentials.
- Modify service factory to create Xfyun services based on configuration.
- Update README with new configuration details for Xfyun integration.
- Add new frontend components for visualizing audio streams and managing user interactions.

backend/services/config_resolver.py

@@ -62,6 +62,8 @@ async def resolve_runtime_config(
         voice=(tts.voice if tts else ""),
         stt_language=(stt.language if stt else ""),
         tts_speed=(tts.speed if tts else 1.0),
+        stt_interface_type=(stt.interface_type if stt else "openai"),
+        tts_interface_type=(tts.interface_type if tts else "openai"),
         realtimeModel=(realtime.model_id if realtime else ""),
         # 运行时连接信息(真 key + url):凭证优先,否则 .env 兜底
         llm_api_key=(llm.api_key if llm else config.LLM_API_KEY),