ML-007: add retraining pipeline and API

Closes #13

app/ml/__init__.py

@@ -1,5 +1,14 @@
 
 """Machine-Learning-Grundbausteine für SillyHome Next."""
-__all__ = ["FeatureStore", "FeatureVector", "TrainedArtifact", "TrainingPipeline"]
+__all__ = [
+    "FeatureStore",
+    "FeatureVector",
+    "RetrainingResult",
+    "RetrainingService",
+    "TrainedArtifact",
+    "TrainingPipeline",
+    "retrain_model",
+]
 from app.ml.feature_store import FeatureStore, FeatureVector
+from app.ml.retraining import RetrainingResult, RetrainingService, retrain_model
 from app.ml.training import TrainedArtifact, TrainingPipeline