fix: add docstring to MetaClassifierService constructor for clarity

app/services/meta_classifier.py

@@ -71,6 +71,7 @@ class MetaClassifierService:
     """
 
     def __init__(self) -> None:
+        """Initialize meta-classifier with empty state."""
         self._model = None
         self._scaler = None
         self._feature_cols: list[str] = []