fix: add docstring to Wav2Vec2DetectorService constructor for clarity

app/services/wav2vec2_detector.py

@@ -48,6 +48,7 @@ class Wav2Vec2DetectorService:
     """
 
     def __init__(self, model_path: Optional[Path] = None) -> None:
+        """Initialize wav2vec2 detector with optional model path."""
         self._model = None
         self._device = None
         self._initialized = False