Fix buffer aliasing and cleanup unused fields in audio

- Copy opus data in ReadMessage to prevent aliasing with internal buffer
- Remove unused ctx field from OutputRelay struct
- Fix OPUS_BANDWIDTH comment accuracy (20kHz passband)

internal/audio/c/audio.c

@@ -88,7 +88,7 @@ static uint16_t max_packet_size = 1500;
 #define OPUS_VBR 1                    // Variable bitrate mode enabled
 #define OPUS_VBR_CONSTRAINT 1         // Constrained VBR maintains bitrate ceiling
 #define OPUS_SIGNAL_TYPE 3002         // OPUS_SIGNAL_MUSIC (optimized for music/audio content)
-#define OPUS_BANDWIDTH 1105           // OPUS_BANDWIDTH_FULLBAND (0-20kHz frequency range)
+#define OPUS_BANDWIDTH 1105           // OPUS_BANDWIDTH_FULLBAND (20kHz passband)
 #define OPUS_LSB_DEPTH 16             // 16-bit PCM sample depth (S16_LE format)
 
 static uint8_t opus_dtx_enabled = 1;

internal/audio/cgo_source.go

@@ -216,7 +216,11 @@ func (c *CgoSource) ReadMessage() (uint8, []byte, error) {
 		return 0, nil, fmt.Errorf("opus packet too large: %d > %d", opusSize, len(c.opusBuf))
 	}
 
-	return ipcMsgTypeOpus, c.opusBuf[:opusSize], nil
+	// Return a copy to prevent buffer aliasing - the caller may hold this slice
+	// while the next ReadMessage overwrites the internal buffer
+	result := make([]byte, opusSize)
+	copy(result, c.opusBuf[:opusSize])
+	return ipcMsgTypeOpus, result, nil
 }
 
 func (c *CgoSource) WriteMessage(msgType uint8, payload []byte) error {

internal/audio/relay.go

@@ -15,7 +15,6 @@ import (
 type OutputRelay struct {
 	source     *AudioSource
 	audioTrack *webrtc.TrackLocalStaticSample
-	ctx        context.Context
 	cancel     context.CancelFunc
 	logger     zerolog.Logger
 	running    atomic.Bool
@@ -27,13 +26,12 @@ type OutputRelay struct {
 }
 
 func NewOutputRelay(source *AudioSource, audioTrack *webrtc.TrackLocalStaticSample) *OutputRelay {
-	ctx, cancel := context.WithCancel(context.Background())
+	_, cancel := context.WithCancel(context.Background())
 	logger := logging.GetDefaultLogger().With().Str("component", "audio-output-relay").Logger()
 
 	return &OutputRelay{
 		source:     source,
 		audioTrack: audioTrack,
-		ctx:        ctx,
 		cancel:     cancel,
 		logger:     logger,
 		stopped:    make(chan struct{}),