fix: update chart risk label

app/prediction.py

@@ -456,7 +456,7 @@ def render_survival_chart(df: pd.DataFrame, curves, image_path: Path) -> tuple[l
 
     font_kwargs = chinese_font_kwargs()
     plt.xlabel("管龄（年）", **font_kwargs)
-    plt.ylabel("生存概率", **font_kwargs)
+    plt.ylabel("健康风险", **font_kwargs)
     plt.title("预测分析图", **font_kwargs)
     plt.grid(alpha=0.18)
     if len(summary_rows) <= 12:

tests/test_prediction.py

@@ -143,16 +143,18 @@ class PredictionHelpersTest(unittest.TestCase):
             self.assertEqual(sample_worksheet["B1"].value, "00123")
             self.assertEqual(sample_worksheet["B1"].data_type, "s")
 
-    def test_survival_chart_uses_pipe_age_x_axis_label(self) -> None:
+    def test_survival_chart_uses_expected_axis_labels(self) -> None:
         df = pd.DataFrame({ID_COLUMN: ["P001"], PIPE_AGE_COLUMN: [12]})
 
         with TemporaryDirectory() as temp_dir:
             output_path = Path(temp_dir) / "chart.png"
-            with patch("app.prediction.plt.xlabel") as xlabel:
+            with patch("app.prediction.plt.xlabel") as xlabel, patch("app.prediction.plt.ylabel") as ylabel:
                 render_survival_chart(df, [DummyCurve([1, 2], [0.9, 0.7])], output_path)
 
         xlabel.assert_called_once()
         self.assertEqual(xlabel.call_args.args[0], "管龄（年）")
+        ylabel.assert_called_once()
+        self.assertEqual(ylabel.call_args.args[0], "健康风险")
 
 
 if __name__ == "__main__":