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_quick_item.py

@@ -0,0 +1,61 @@
+"""Tests for src/pygui/backend/visualization/graph_quick_item.py."""
+import pytest
+
+pytestmark = pytest.mark.usefixtures("qapp")
+
+
+def test_no_data_initially():
+    from pygui.backend.visualization.graph_quick_item import GraphQuickItem
+
+    item = GraphQuickItem()
+    assert item.seriesData == []
+    assert item.sensorNames == []
+
+
+def test_series_data_setter_stores_series():
+    from pygui.backend.visualization.graph_quick_item import GraphQuickItem
+
+    item = GraphQuickItem()
+    item.seriesData = [[150.0, 151.0], [148.0, 147.5]]
+
+    assert item.seriesData == [[150.0, 151.0], [148.0, 147.5]]
+
+
+def test_series_data_auto_ranges_y_with_padding():
+    from pygui.backend.visualization.graph_quick_item import GraphQuickItem
+
+    item = GraphQuickItem()
+    item.seriesData = [[150.0, 100.0], [200.0, 120.0]]
+
+    # min=100, max=200, range=100, 10% pad => [90, 210]
+    assert item._min_y == pytest.approx(90.0)
+    assert item._max_y == pytest.approx(210.0)
+
+
+def test_series_data_empty_keeps_default_range():
+    from pygui.backend.visualization.graph_quick_item import GraphQuickItem
+
+    item = GraphQuickItem()
+    item.seriesData = []
+
+    assert item._min_y == 0.0
+    assert item._max_y == 150.0
+
+
+def test_sensor_names_setter_stores_names():
+    from pygui.backend.visualization.graph_quick_item import GraphQuickItem
+
+    item = GraphQuickItem()
+    item.sensorNames = ["Sensor 1", "Sensor 2"]
+
+    assert item.sensorNames == ["Sensor 1", "Sensor 2"]
+
+
+def test_non_numeric_values_are_skipped_not_crashing():
+    from pygui.backend.visualization.graph_quick_item import GraphQuickItem
+
+    item = GraphQuickItem()
+    item.seriesData = [[150.0, "bad", 151.0]]
+
+    assert item._min_y == pytest.approx(149.9)
+    assert item._max_y == pytest.approx(151.1)