Add server api definition

MusicCast.Net.Api.Server/Models/GetSignalInfoResponse.cs

@@ -0,0 +1,14 @@
+namespace MusicCast.Net.Api.Server.Models;
+
+public class GetSignalInfoResponse
+{
+    public int response_code { get; set; }
+    public Audio audio { get; set; }
+
+    public class Audio
+    {
+        public int error { get; set; }
+        public string format { get; set; }
+        public string fs { get; set; }
+    }
+}