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.

frontend/src/hooks/use-voice-preview.ts

@@ -74,6 +74,8 @@ export function useVoicePreview(assistantId: string | null) {
   const [error, setError] = useState<string | null>(null);
   const [micWarning, setMicWarning] = useState<string | null>(null);
   const [localStream, setLocalStream] = useState<MediaStream | null>(null);
+  // 远端(助手 TTS)媒体流:除挂到 <audio> 播放外,也暴露给波形可视化
+  const [remoteStream, setRemoteStream] = useState<MediaStream | null>(null);
   const [messages, setMessages] = useState<ChatMessage[]>([]);
   // 可选麦克风列表与当前选择(空串表示交给浏览器选默认设备)
   const [audioInputs, setAudioInputs] = useState<MediaDeviceInfo[]>([]);
@@ -92,7 +94,8 @@ export function useVoicePreview(assistantId: string | null) {
     if (!navigator.mediaDevices?.enumerateDevices) return;
     try {
       const devices = await navigator.mediaDevices.enumerateDevices();
-      const inputs = devices.filter((d) => d.kind === "audioinput");
+      // 未授权时设备可能没有 deviceId(空串),无法选择,直接过滤掉
+      const inputs = devices.filter((d) => d.kind === "audioinput" && d.deviceId);
       setAudioInputs(inputs);
       // 选中的设备已被拔出时,回退到浏览器默认设备
       if (
@@ -157,6 +160,7 @@ export function useVoicePreview(assistantId: string | null) {
   const disconnect = useCallback(() => {
     releaseResources();
     setLocalStream(null);
+    setRemoteStream(null);
     setError(null);
     setMicWarning(null);
     setStatus("idle");
@@ -166,6 +170,7 @@ export function useVoicePreview(assistantId: string | null) {
     (message: string) => {
       releaseResources();
       setLocalStream(null);
+      setRemoteStream(null);
       setError(message);
       setStatus("failed");
     },
@@ -312,9 +317,11 @@ export function useVoicePreview(assistantId: string | null) {
       };
 
       pc.ontrack = (e) => {
-        if (e.track.kind === "audio" && audioRef.current) {
-          audioRef.current.srcObject =
-            e.streams[0] ?? new MediaStream([e.track]);
+        if (e.track.kind !== "audio") return;
+        const remote = e.streams[0] ?? new MediaStream([e.track]);
+        setRemoteStream(remote);
+        if (audioRef.current) {
+          audioRef.current.srcObject = remote;
           void audioRef.current.play().catch(() => {});
         }
       };
@@ -384,6 +391,7 @@ export function useVoicePreview(assistantId: string | null) {
     error,
     micWarning,
     localStream,
+    remoteStream,
     messages,
     audioInputs,
     selectedDeviceId,