fix(recognition): prevent stop sound from being transcribed (#150)

When stopping voice recognition, the stop sound was being captured by the
microphone and transcribed as "thank you" or similar text. This happened
because the sound was played BEFORE stopping recording.

Fix:
- Stop recording FIRST by setting should_record = False
- Wait briefly for audio thread to stop
- Discard the last ~1 second of audio buffer (15 chunks) which would
  contain the feedback sound
- THEN play the stop sound after recording has stopped
- Process remaining valid audio

This ensures that audio captured during the stop sound is discarded and
won't be transcribed.

Technical details:
- Audio recorded in 1024-sample chunks at 16000 Hz = ~64ms per chunk
- Discarding 15 chunks = ~960ms of audio
- Uses existing _buffer_lock for thread safety

Closes #150

src/vocalinux/speech_recognition/recognition_manager.py

@@ -921,12 +921,31 @@ class SpeechRecognitionManager:
 
         logger.info("Stopping speech recognition")
 
-        # Play the stop sound
-        play_stop_sound()
-
-        # Clear recording flag
+        # Stop recording FIRST to prevent capturing the stop sound
         self.should_record = False
 
+        # Wait briefly for audio thread to stop recording
+        if self.audio_thread and self.audio_thread.is_alive():
+            self.audio_thread.join(timeout=0.1)
+
+        # Discard the last ~1 second of audio to avoid transcribing the stop sound
+        # Audio is recorded in 1024-sample chunks at 16000 Hz = ~64ms per chunk
+        # We discard the last 15 chunks (~1 second) which should contain the feedback sound
+        with self._buffer_lock:
+            if len(self.audio_buffer) > 15:
+                discarded_chunks = self.audio_buffer[-15:]
+                self.audio_buffer = self.audio_buffer[:-15]
+                logger.debug(
+                    f"Discarded {len(discarded_chunks)} audio chunks to avoid transcribing feedback sound"
+                )
+            elif self.audio_buffer:
+                # If buffer is small, just clear it entirely to be safe
+                logger.debug(f"Clearing small audio buffer ({len(self.audio_buffer)} chunks)")
+                self.audio_buffer = []
+
+        # Now play the stop sound (after recording has stopped)
+        play_stop_sound()
+
         # Wait for threads to finish
         if self.audio_thread and self.audio_thread.is_alive():
             self.audio_thread.join(timeout=1.0)