Add system mute control via setMute action

Introduce a setMute protocol action and an NAudio-backed
AudioControlService so the Android client can toggle the Windows
render endpoint mute state over WebSocket.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

WirelessTextSyncer.Windows/Services/AudioControlService.cs

@@ -0,0 +1,52 @@
+using System.Runtime.InteropServices;
+using NAudio.CoreAudioApi;
+
+namespace WirelessTextSyncer.Windows.Services;
+
+public sealed class AudioControlService : IAudioControlService, IDisposable
+{
+    private readonly MMDeviceEnumerator enumerator = new();
+    private bool disposed;
+
+    public bool IsMuted
+    {
+        get
+        {
+            try
+            {
+                using var device = enumerator.GetDefaultAudioEndpoint(DataFlow.Render, Role.Multimedia);
+                return device.AudioEndpointVolume.Mute;
+            }
+            catch (COMException exception)
+            {
+                AppLogger.Error("Failed to read audio mute state.", exception);
+                return false;
+            }
+        }
+    }
+
+    public void SetMute(bool muted)
+    {
+        try
+        {
+            using var device = enumerator.GetDefaultAudioEndpoint(DataFlow.Render, Role.Multimedia);
+            device.AudioEndpointVolume.Mute = muted;
+            AppLogger.Info($"Audio mute set to {muted}.");
+        }
+        catch (COMException exception)
+        {
+            AppLogger.Error($"Failed to set audio mute to {muted}.", exception);
+        }
+    }
+
+    public void Dispose()
+    {
+        if (disposed)
+        {
+            return;
+        }
+
+        disposed = true;
+        enumerator.Dispose();
+    }
+}