Improve meeting audio mixing pipeline

MeetingAssistant/MeetingAssistantOptions.cs

@@ -114,6 +114,10 @@ public sealed class RecordingOptions
 
     public int Channels { get; set; } = 1;
 
+    public double MicrophoneMixGain { get; set; } = 1;
+
+    public double SystemAudioMixGain { get; set; } = 1;
+
     public TimeSpan StopProcessingTimeout { get; set; } = TimeSpan.FromMinutes(10);
 
     public TimeSpan MetadataLookupTimeout { get; set; } = TimeSpan.FromSeconds(10);