ML-007: add retraining pipeline and API

Closes #13

tests/ml/test_model_registry.py

@@ -19,6 +19,17 @@ def test_registry_loads_persisted_artifacts_after_restart(tmp_path: Path) -> Non
     assert restarted.load_artifact("model-v1") == artifact
 
 
+def test_registry_replaces_persisted_artifact_after_restart(tmp_path: Path) -> None:
+    registry = ModelRegistry(tmp_path)
+    registry.register(TrainedArtifact("model-v1", ("sensor.kitchen",)))
+    replacement = TrainedArtifact("model-v1", ("sensor.bedroom",))
+
+    registry.register(replacement)
+
+    assert registry.load_artifact("model-v1") == replacement
+    assert ModelRegistry(tmp_path).load_artifact("model-v1") == replacement
+
+
 @pytest.mark.parametrize("artifact_id", ["../escape", "nested/model", "..", ""])
 def test_registry_rejects_unsafe_artifact_ids(tmp_path: Path, artifact_id: str) -> None:
     registry = ModelRegistry(tmp_path)