feat(graph): add graph tab for whole-run data

Provides a static line chart plotting multi-sensor temperature values
over time when a session file is loaded.

tests/test_graph_view.py

@@ -66,6 +66,51 @@ class TestUpdateTrend:
         gv.updateTrend("[1, 2, 3]")
 
 
+class TestUpdateChart:
+    def test_plots_one_series_per_sensor(self):
+        from pygui.backend.visualization.graph_view import GraphView
+
+        gv = GraphView()
+        gv._plot_widget = _make_plot_widget()
+
+        series = [[150.0, 151.0, 152.0], [148.5, 148.4, 148.6]]
+        gv.updateChart("Sensor 1,Sensor 2", json.dumps(series))
+
+        assert gv._plot_widget.clear.called
+        assert gv._plot_widget.plot.call_count == 2
+        assert gv._sensor_names == ["Sensor 1", "Sensor 2"]
+
+    def test_rejects_invalid_json(self):
+        from pygui.backend.visualization.graph_view import GraphView
+
+        gv = GraphView()
+        gv._plot_widget = _make_plot_widget()
+
+        gv.updateChart("Sensor 1", "not json")
+
+        assert not gv._plot_widget.plot.called
+
+    def test_empty_series_clears_without_plotting(self):
+        from pygui.backend.visualization.graph_view import GraphView
+
+        gv = GraphView()
+        gv._plot_widget = _make_plot_widget()
+
+        gv.updateChart("", "[]")
+
+        assert gv._plot_widget.clear.called
+        assert not gv._plot_widget.plot.called
+
+    def test_no_plot_widget(self):
+        from pygui.backend.visualization.graph_view import GraphView
+
+        gv = GraphView()
+        assert gv._plot_widget is None
+
+        # Should not crash
+        gv.updateChart("Sensor 1", json.dumps([[1.0, 2.0]]))
+
+
 class TestUpdateComparison:
     def test_parses_valid_json(self):
         from pygui.backend.visualization.graph_view import GraphView