feat: named case-result load combinations with full GUI support

Snapshots the current development tree, headlined by proper load
combinations (user request): a reusable LoadCombination entity of
weighted completed static-case results (e.g. 1.2xDead + 1.6xLive).

- core: LoadCombination/LoadCombinationItem entities, Project
  integration (lookup, unique ids, reference validation)
- services: combinations.py (linear superposition + envelope),
  exported via services __init__
- commands: undoable Add/Delete/Update for combinations
- GUI: Load Combinations manager dialog, Run-dialog evaluation,
  envelope display in Results panel, Combinations tab in Table dock
- tests: unit coverage (validation, math, error paths) + integration
  superposition check vs a single factored run

tests/gui/test_pushover_curve_units.py

@@ -0,0 +1,107 @@
+"""Pushover curve axis labels must follow the project's unit system."""
+
+from __future__ import annotations
+
+import numpy as np
+import pytest
+
+pytest.importorskip("PySide6")
+
+from otko.core import UnitSystem  # noqa: E402
+from otko.services.results import PushoverResults  # noqa: E402
+from otko.views.docks.pushover_curve import (  # noqa: E402
+    PushoverCurveView,
+    _is_rotation_dof,
+)
+
+
+def _pushover(control_dof: int = 1) -> PushoverResults:
+    return PushoverResults(
+        case_id=1,
+        case_name="tst",
+        n_steps=5,
+        control_node=2,
+        control_dof=control_dof,
+        control_disp=np.array([0.0, 1.0, 2.0, 3.0, 4.0, 5.0]),
+        base_shear=np.array([0.0, 100.0, 200.0, 300.0, 400.0, 500.0]),
+    )
+
+
+def test_is_rotation_dof_ndf3() -> None:
+    """In a 2D/ndf=3 model, only DOF 3 is rotational."""
+    assert _is_rotation_dof(1, ndf=3) is False
+    assert _is_rotation_dof(2, ndf=3) is False
+    assert _is_rotation_dof(3, ndf=3) is True
+
+
+def test_is_rotation_dof_ndf6() -> None:
+    """In a 3D/ndf=6 model, DOFs 4, 5, 6 are rotational."""
+    assert _is_rotation_dof(1, ndf=6) is False
+    assert _is_rotation_dof(3, ndf=6) is False  # Uz in 3D
+    assert _is_rotation_dof(4, ndf=6) is True  # Rx
+    assert _is_rotation_dof(5, ndf=6) is True  # Ry
+    assert _is_rotation_dof(6, ndf=6) is True  # Rz
+
+
+@pytest.mark.gui
+def test_si_translation_labels(qtbot) -> None:  # type: ignore[no-untyped-def]
+    v = PushoverCurveView(units=UnitSystem.SI_M_N, ndf=6)
+    qtbot.addWidget(v)
+    v.set_results(_pushover(control_dof=1))
+    assert "m" in v._plot.getAxis("bottom").labelText
+    assert "Displacement" in v._plot.getAxis("bottom").labelText
+    assert "N" in v._plot.getAxis("left").labelText
+    assert "Base shear" in v._plot.getAxis("left").labelText
+
+
+@pytest.mark.gui
+def test_si_rotation_labels_show_curvature_and_moment(qtbot) -> None:  # type: ignore[no-untyped-def]
+    v = PushoverCurveView(units=UnitSystem.SI_M_N, ndf=3)
+    qtbot.addWidget(v)
+    v.set_results(_pushover(control_dof=3))
+    assert "1/m" in v._plot.getAxis("bottom").labelText
+    assert "Curvature" in v._plot.getAxis("bottom").labelText
+    assert "N·m" in v._plot.getAxis("left").labelText
+    assert "Moment" in v._plot.getAxis("left").labelText
+
+
+@pytest.mark.gui
+def test_us_in_kip_rotation_labels(qtbot) -> None:  # type: ignore[no-untyped-def]
+    """kip-in Moment-Curvature project must NOT show cm / kN anywhere."""
+    v = PushoverCurveView(units=UnitSystem.US_IN_KIP, ndf=3)
+    qtbot.addWidget(v)
+    v.set_results(_pushover(control_dof=3))
+    x_label = v._plot.getAxis("bottom").labelText
+    y_label = v._plot.getAxis("left").labelText
+    assert "1/in" in x_label
+    assert "kip·in" in y_label
+    assert "cm" not in x_label
+    assert "kN" not in y_label
+
+
+@pytest.mark.gui
+def test_us_in_kip_translation_labels(qtbot) -> None:  # type: ignore[no-untyped-def]
+    v = PushoverCurveView(units=UnitSystem.US_IN_KIP, ndf=3)
+    qtbot.addWidget(v)
+    v.set_results(_pushover(control_dof=1))
+    assert "in" in v._plot.getAxis("bottom").labelText
+    assert "kip" in v._plot.getAxis("left").labelText
+
+
+@pytest.mark.gui
+def test_no_auto_scaling_applied_to_values(qtbot) -> None:  # type: ignore[no-untyped-def]
+    """Regression: earlier versions divided base_shear by 1000 to
+    display kN. The values must now be drawn exactly as stored so
+    kip-in users don't see nonsense scaling."""
+    v = PushoverCurveView(units=UnitSystem.US_IN_KIP, ndf=3)
+    qtbot.addWidget(v)
+    r = _pushover(control_dof=3)
+    v.set_results(r)
+    # Take the single line item that was added; the item's data
+    # should match the input arrays point-for-point.
+    items = [it for it in v._plot.listDataItems() if hasattr(it, "getData")]
+    assert items, "Pushover curve has no plot items"
+    xs, ys = items[0].getData()
+    # The first line item is the actual data (reference line is second).
+    np.testing.assert_allclose(xs, r.control_disp)
+    np.testing.assert_allclose(ys, r.base_shear)