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_run_analysis.py

@@ -0,0 +1,76 @@
+"""GUI tests for the Run Analysis dialog."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+pytest.importorskip("PySide6")
+
+from PySide6.QtCore import QObject, Signal  # noqa: E402
+
+from otko.core import LinearTimeSeries, PlainLoadPattern, Project, TransientCase  # noqa: E402
+from otko.viewmodels import ProjectViewModel  # noqa: E402
+from otko.views.dialogs.run_analysis import RunAnalysisDialog  # noqa: E402
+
+
+class _FakeRunner(QObject):
+    started = Signal()
+    log = Signal(str)
+    finished = Signal(object)
+    failed = Signal(str)
+    runningChanged = Signal(bool)
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.is_running = False
+        self.last_project = None
+        self.last_case = None
+        self.last_results_dir = None
+
+    def run(self, project, case, results_dir=None) -> None:  # type: ignore[no-untyped-def]
+        self.last_project = project
+        self.last_case = case
+        self.last_results_dir = results_dir
+
+
+@pytest.mark.gui
+def test_run_dialog_applies_transient_damping_overrides(qtbot, tmp_path) -> None:  # type: ignore[no-untyped-def]
+    vm = ProjectViewModel()
+    vm.new_project()
+    vm.project.time_series.append(LinearTimeSeries(id=1, name="Ramp"))  # type: ignore[union-attr]
+    vm.project.load_patterns.append(PlainLoadPattern(id=1, name="P1", time_series_id=1))  # type: ignore[union-attr]
+    vm.project.analyses.append(
+        TransientCase(  # type: ignore[union-attr]
+            id=1,
+            name="EQ",
+            pattern_ids=[1],
+            dt=0.01,
+            n_steps=10,
+            rayleigh_alpha_m=0.1,
+            rayleigh_beta_k=0.002,
+            rayleigh_mode1_damping=0.02,
+        )
+    )
+    vm._path = Path(tmp_path) / "demo.osmodel"  # type: ignore[attr-defined]
+
+    runner = _FakeRunner()
+    dlg = RunAnalysisDialog(vm, runner)
+    qtbot.addWidget(dlg)
+
+    dlg._case_combo.setCurrentIndex(0)
+    assert dlg._alpha_m.value() == pytest.approx(0.1)
+    assert dlg._beta_k.value() == pytest.approx(0.002)
+    assert dlg._mode1_damping.value() == pytest.approx(0.02)
+
+    dlg._alpha_m.setValue(0.3)
+    dlg._beta_k.setValue(0.005)
+    dlg._mode1_damping.setValue(0.05)
+    dlg._on_run()
+
+    assert runner.last_project is vm.project
+    assert runner.last_case.rayleigh_alpha_m == pytest.approx(0.3)
+    assert runner.last_case.rayleigh_beta_k == pytest.approx(0.005)
+    assert runner.last_case.rayleigh_mode1_damping == pytest.approx(0.05)
+    assert runner.last_results_dir == tmp_path / "demo_results"