ML-009: add explainable predictions

Closes #20

tests/ml/test_predictor.py

@@ -33,6 +33,11 @@ def test_predict_returns_statistical_forecast() -> None:
     assert result.predictions == {"temperature": 22.0}
     assert 0.0 < result.confidence <= 1.0
     assert result.model_type == "statistical_baseline"
+    explanation = result.explanations["temperature"]
+    assert explanation.direction == "steigend"
+    assert explanation.current_value == 21.0
+    assert explanation.predicted_value == 22.0
+    assert explanation.sample_count == 2
 
 
 def test_predict_rejects_unknown_sensor() -> None: