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/Tray/TrayApplicationContext.cs

@@ -5,6 +5,7 @@ namespace WirelessTextSyncer.Windows.Tray;
 public sealed class TrayApplicationContext : ApplicationContext
 {
     private readonly KeyboardInjectionService keyboard;
+    private readonly AudioControlService audio;
     private readonly WebSocketServerService server;
     private readonly DiscoveryResponderService discovery;
     private readonly NotifyIcon notifyIcon;
@@ -21,7 +22,8 @@ public sealed class TrayApplicationContext : ApplicationContext
         AppLogger.Info("Tray application starting.");
         uiContext = SynchronizationContext.Current ?? new WindowsFormsSynchronizationContext();
         keyboard = new KeyboardInjectionService();
-        var handler = new SyncMessageHandler(keyboard);
+        audio = new AudioControlService();
+        var handler = new SyncMessageHandler(keyboard, audio);
 
         server = new WebSocketServerService(handler);
         server.StatusChanged += (_, _) => uiContext.Post(_ => UpdateTrayStatus(), null);
@@ -62,6 +64,7 @@ public sealed class TrayApplicationContext : ApplicationContext
             connectedIcon.Dispose();
             waitIcon.Dispose();
             discovery.Dispose();
+            audio.Dispose();
             server.Dispose();
         }