ML-008: add statistical baseline model

Closes #19

app/ml/__init__.py

@@ -3,6 +3,9 @@
 __all__ = [
     "FeatureStore",
     "FeatureVector",
+    "FeatureModel",
+    "PredictionResult",
+    "Predictor",
     "RetrainingResult",
     "RetrainingService",
     "TrainedArtifact",
@@ -10,5 +13,6 @@ __all__ = [
     "retrain_model",
 ]
 from app.ml.feature_store import FeatureStore, FeatureVector
+from app.ml.predictor import PredictionResult, Predictor
 from app.ml.retraining import RetrainingResult, RetrainingService, retrain_model
-from app.ml.training import TrainedArtifact, TrainingPipeline
+from app.ml.training import FeatureModel, TrainedArtifact, TrainingPipeline