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/Models/SyncAction.cs

@@ -9,5 +9,6 @@ public enum SyncAction
     ReplaceAll,
     Backspace,
     Enter,
-    Ping
+    Ping,
+    SetMute
 }

WirelessTextSyncer.Windows/Models/SyncActionJsonConverter.cs

@@ -19,6 +19,7 @@ public sealed class SyncActionJsonConverter : JsonConverter<SyncAction>
             "backspace" => SyncAction.Backspace,
             "enter" => SyncAction.Enter,
             "ping" => SyncAction.Ping,
+            "setMute" => SyncAction.SetMute,
             _ => throw new JsonException($"Unsupported sync action: {value}")
         };
     }
@@ -35,6 +36,7 @@ public sealed class SyncActionJsonConverter : JsonConverter<SyncAction>
             SyncAction.Backspace => "backspace",
             SyncAction.Enter => "enter",
             SyncAction.Ping => "ping",
+            SyncAction.SetMute => "setMute",
             _ => throw new JsonException($"Unsupported sync action: {value}")
         };
 

WirelessTextSyncer.Windows/Models/SyncMessage.cs

@@ -9,4 +9,7 @@ public sealed record SyncMessage
 
     [JsonPropertyName("text")]
     public string? Text { get; init; }
+
+    [JsonPropertyName("muted")]
+    public bool? Muted { get; init; }
 }