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_property_forms.py

@@ -0,0 +1,130 @@
+"""Unit tests for material and section parameter forms.
+
+Each form must satisfy a round-trip property: ``form.populate(m); m2 = form.read()``
+yields ``m2 == m`` (modulo any None defaults the form's spinbox can't represent).
+"""
+
+from __future__ import annotations
+
+import pytest
+
+pytest.importorskip("PySide6")
+
+from otko.core import (  # noqa: E402
+    Concrete01,
+    Concrete02,
+    ElasticIsotropic,
+    ElasticPP,
+    ElasticSection,
+    ElasticUniaxial,
+    Steel01,
+    Steel02,
+)
+
+
+@pytest.mark.gui
+def test_steel01_form_round_trip(qtbot) -> None:  # type: ignore[no-untyped-def]
+    from otko.views.dialogs.material_forms import Steel01Form
+
+    original = Steel01(id=7, name="MyS420", Fy=420e6, E0=200e9, b=0.015)
+    form = Steel01Form()
+    form.populate(original)
+    restored = form.read()
+    assert restored == original
+
+
+@pytest.mark.gui
+def test_steel02_form_round_trip(qtbot) -> None:  # type: ignore[no-untyped-def]
+    from otko.views.dialogs.material_forms import Steel02Form
+
+    original = Steel02(id=3, name="S355", Fy=355e6, E0=210e9, b=0.005, R0=18.0, cR1=0.925, cR2=0.15)
+    form = Steel02Form()
+    form.populate(original)
+    restored = form.read()
+    assert restored == original
+
+
+@pytest.mark.gui
+def test_concrete02_form_round_trip(qtbot) -> None:  # type: ignore[no-untyped-def]
+    from otko.views.dialogs.material_forms import Concrete02Form
+
+    original = Concrete02(
+        id=2,
+        name="C30",
+        fpc=-30e6,
+        epsc0=-0.002,
+        fpcu=-15e6,
+        epsU=-0.005,
+        ft=3e6,
+        Ets=2e9,
+        **{"lambda": 0.1},
+    )
+    form = Concrete02Form()
+    form.populate(original)
+    restored = form.read()
+    assert restored == original
+
+
+@pytest.mark.gui
+def test_elastic_isotropic_form_round_trip(qtbot) -> None:  # type: ignore[no-untyped-def]
+    from otko.views.dialogs.material_forms import ElasticIsotropicForm
+
+    original = ElasticIsotropic(id=1, name="Steel", E=200e9, nu=0.3, rho=7850.0)
+    form = ElasticIsotropicForm()
+    form.populate(original)
+    restored = form.read()
+    assert restored == original
+
+
+@pytest.mark.gui
+def test_elastic_section_form_round_trip(qtbot) -> None:  # type: ignore[no-untyped-def]
+    from otko.views.dialogs.section_forms import ElasticSectionForm
+
+    original = ElasticSection(
+        id=11,
+        name="W14x90",
+        E=200e9,
+        A=0.017,
+        Iz=4.16e-4,
+        Iy=1.29e-4,
+        G=80e9,
+        J=2.04e-6,
+    )
+    form = ElasticSectionForm()
+    form.populate(original)
+    restored = form.read()
+    assert restored == original
+
+
+@pytest.mark.gui
+def test_form_for_dispatches_by_type(qtbot) -> None:  # type: ignore[no-untyped-def]
+    from otko.views.dialogs.material_forms import (
+        Steel01Form,
+        form_for as material_form_for,
+    )
+    from otko.views.dialogs.section_forms import (
+        ElasticSectionForm,
+        form_for as section_form_for,
+    )
+
+    s = Steel01(id=1, Fy=420e6, E0=200e9, b=0.01)
+    f = material_form_for(s)
+    assert isinstance(f, Steel01Form)
+
+    es = ElasticSection(id=1, E=200e9, A=0.01, Iz=1e-5)
+    f2 = section_form_for(es)
+    assert isinstance(f2, ElasticSectionForm)
+
+
+@pytest.mark.gui
+def test_unknown_material_type_raises(qtbot) -> None:  # type: ignore[no-untyped-def]
+    """form_for raises KeyError for unsupported types."""
+    from otko.views.dialogs.material_forms import form_for
+
+    class FakeMat:
+        type = "Unobtanium"
+        id = 1
+        name = ""
+
+    with pytest.raises(KeyError):
+        form_for(FakeMat())