audio: add deafened property to suppress playback

When deafened, playback callback writes silence and
queue_playback discards incoming PCM.

tests/test_audio.py

@@ -10,6 +10,7 @@ def test_default_construction():
     assert ap._input_device is None
     assert ap._output_device is None
     assert ap.capturing is False
+    assert ap.deafened is False
 
 
 def test_custom_construction():
@@ -89,6 +90,37 @@ def test_queue_playback_overflow_drops():
     assert ap._playback_queue.qsize() == ap._playback_queue.maxsize
 
 
+def test_deafened_toggle():
+    ap = AudioPipeline()
+    assert ap.deafened is False
+    ap.deafened = True
+    assert ap.deafened is True
+    ap.deafened = False
+    assert ap.deafened is False
+
+
+def test_queue_playback_discards_when_deafened():
+    """Incoming PCM is dropped when deafened."""
+    ap = AudioPipeline()
+    ap.deafened = True
+    ap.queue_playback(b"\x42" * 100)
+    assert ap._playback_queue.qsize() == 0
+
+
+def test_playback_callback_silence_when_deafened():
+    """Playback callback writes silence when deafened, even with queued data."""
+    ap = AudioPipeline()
+    frame_bytes = FRAME_SIZE * 2
+    # Queue data before deafening
+    pcm = b"\x42" * frame_bytes
+    ap.queue_playback(pcm)
+    ap.deafened = True
+
+    outdata = bytearray(b"\xff" * frame_bytes)
+    ap._playback_callback(outdata, FRAME_SIZE, None, None)
+    assert outdata == bytearray(frame_bytes)  # all zeros
+
+
 def test_stop_without_start():
     """Stop on unstarted pipeline should not raise."""
     ap = AudioPipeline()