Add --tone-test mode: 440 Hz Opus tone + incoming audio capture

Adds a --tone-test flag that bypasses all OpenAL/soundcard
initialization and instead:

- Generates a 440 Hz sine wave at 48kHz mono, encodes it via Opus,
  and sends it to the Mumble server.

- Saves all incoming decoded audio to a raw PCM file (s16le,
  stereo, 48kHz) specified by --tone-out (default: incoming.pcm).

Useful for end-to-end testing of the Opus encode/decode pipeline
and Mumble transport without requiring physical audio hardware.

Usage:
  barnard --server HOST --tone-test --tone-out /tmp/in.pcm

  ffplay -f s16le -ar 48000 -ac 2 incoming.pcm

client.go

@@ -17,11 +17,18 @@ func (b *Barnard) start() {
 	b.Config.Attach(gumbleutil.AutoBitrate)
 	b.Config.Attach(b)
 	b.Config.Address = b.Address
-	// test Audio
-	_, err := gumbleopenal.New(b.Client, b.UserConfig.GetInputDevice(), b.UserConfig.GetOutputDevice(), true)
-	if err != nil {
-		b.exitWithError(err)
-		return
+
+	if b.ToneTest {
+		// Tone test mode: skip all OpenAL/soundcard initialization.
+		// We just need a network connection — the tone generator and
+		// file saver are set up in connect().
+	} else {
+		// test Audio
+		_, err := gumbleopenal.New(b.Client, b.UserConfig.GetInputDevice(), b.UserConfig.GetOutputDevice(), true)
+		if err != nil {
+			b.exitWithError(err)
+			return
+		}
 	}
 	//connect, not reconnect
 	b.connect(false)
@@ -45,6 +52,27 @@ func (b *Barnard) connect(reconnect bool) bool {
 		return false
 	}
 
+	if b.ToneTest {
+		// --- Tone test mode: skip all OpenAL; generate 440 Hz tone
+		// --- and save incoming audio to a file.
+
+		// Start the tone generator goroutine.
+		b.toneTestStop = make(chan struct{})
+		go StartToneGenerator(b.Client, b.toneTestStop)
+
+		// Attach the audio file saver.
+		saver, err := NewAudioFileSaver(b.ToneTestOutput)
+		if err != nil {
+			b.exitWithError(err)
+			return false
+		}
+		b.toneTestSaver = saver
+		b.Client.Config.AttachAudio(saver)
+
+		b.Connected = true
+		return true
+	}
+
 	stream, err := gumbleopenal.New(b.Client, b.UserConfig.GetInputDevice(), b.UserConfig.GetOutputDevice(), false)
 	if err != nil {
 		b.exitWithError(err)
@@ -138,6 +166,19 @@ func (b *Barnard) OnDisconnect(e *gumble.DisconnectEvent) {
 		reason = e.String
 	}
 	b.stopRecordingForDisconnect()
+
+	// Tone test cleanup
+	if b.ToneTest {
+		if b.toneTestStop != nil {
+			close(b.toneTestStop)
+			b.toneTestStop = nil
+		}
+		if b.toneTestSaver != nil {
+			b.toneTestSaver.Stop()
+			b.toneTestSaver = nil
+		}
+	}
+
 	b.Notify("disconnect", "me", reason)
 	if reason == "" {
 		b.AddOutputLine("Disconnected")