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/services/test_imposed_support_motion.py

@@ -0,0 +1,193 @@
+"""ImposedSupportMotionPattern — model validation + runner command emission.
+
+The emission tests inject a ``MagicMock`` as the ops module (the
+``test_runner_translation.py`` pattern); the physics itself is verified in
+``tests/integration/test_runner_imposed_motion.py`` against a uniform-
+excitation reference.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock
+
+import numpy as np
+import pytest
+
+from otko.core import (
+    ElasticUniaxial,
+    ImposedSupportMotionPattern,
+    Node,
+    PathTimeSeries,
+    Project,
+    ZeroLengthElement,
+)
+from otko.services.opensees_runner import (
+    _IMPOSED_VEL_TS_OFFSET,
+    OpenSeesRunner,
+)
+
+
+def _project(**overrides) -> Project:  # type: ignore[no-untyped-def]
+    """Grounded zeroLength + mass node, disp record on the support's X."""
+    defaults = dict(
+        ndm=3,
+        ndf=6,
+        nodes=[
+            Node(id=1, coords=(0, 0, 0), restraint=(True,) * 6),
+            Node(
+                id=2,
+                coords=(0, 0, 0),
+                restraint=(False, True, True, True, True, True),
+                mass=(1.0, 0.0, 0.0, 0.0, 0.0, 0.0),
+            ),
+        ],
+        materials=[ElasticUniaxial(id=1, E=100.0)],
+        elements=[
+            ZeroLengthElement(
+                id=1,
+                nodes=(1, 2),
+                material_ids=(1,),
+                dofs=(1,),
+            )
+        ],
+        time_series=[
+            PathTimeSeries(id=1, dt=0.1, values=[0.0, 1.0, 4.0, 9.0, 16.0]),
+        ],
+        load_patterns=[
+            ImposedSupportMotionPattern(
+                id=7,
+                direction=1,
+                disp_series_id=1,
+                node_ids=[1],
+            )
+        ],
+    )
+    defaults.update(overrides)
+    return Project(**defaults)
+
+
+# ───────────────────────── model / references ─────────────────────────
+def test_round_trip_preserves_pattern() -> None:
+    project = _project()
+    clone = Project.model_validate(project.model_dump())
+    pat = clone.load_patterns[0]
+    assert isinstance(pat, ImposedSupportMotionPattern)
+    assert pat.direction == 1
+    assert pat.disp_series_id == 1
+    assert pat.node_ids == [1]
+
+
+def test_validate_references_missing_series_and_node() -> None:
+    project = _project()
+    project.load_patterns[0].disp_series_id = 99
+    with pytest.raises(ValueError, match="missing time series 99"):
+        project.validate_references()
+
+    project = _project()
+    project.load_patterns[0].node_ids = [42]
+    with pytest.raises(ValueError, match="drives missing node 42"):
+        project.validate_references()
+
+
+# ───────────────────────── emission ─────────────────────────
+def _emit(project: Project) -> MagicMock:
+    ops = MagicMock()
+    runner = OpenSeesRunner(project, ops_module=ops)
+    runner._emit_patterns_for_case([7])
+    return ops
+
+
+def test_emission_sequence() -> None:
+    ops = _emit(_project())
+
+    # Derived velocity series: central differences of the disp record.
+    ts_calls = ops.timeSeries.call_args_list
+    assert ts_calls[0].args[:2] == ("Path", 1)  # the disp record itself
+    kind, tag, flag_dt, dt, flag_vals, *rest = ts_calls[1].args
+    assert (kind, tag, flag_dt, dt, flag_vals) == (
+        "Path",
+        _IMPOSED_VEL_TS_OFFSET + 7,
+        "-dt",
+        0.1,
+        "-values",
+    )
+    vel = rest[: rest.index("-factor")]
+    expected = np.gradient(np.array([0.0, 1.0, 4.0, 9.0, 16.0]), 0.1)
+    assert np.allclose(vel, expected)
+
+    # The X fix is swapped for the imposed motion, then the pattern lands.
+    ops.remove.assert_called_once_with("sp", 1, 1)
+    ops.pattern.assert_called_once_with("MultipleSupport", 7)
+    ops.groundMotion.assert_called_once_with(
+        7,
+        "Plain",
+        "-disp",
+        1,
+        "-vel",
+        _IMPOSED_VEL_TS_OFFSET + 7,
+        "-fact",
+        1.0,
+    )
+    ops.imposedMotion.assert_called_once_with(1, 1, 7)
+
+
+def test_emission_order_fix_removed_before_pattern() -> None:
+    ops = _emit(_project())
+    names = [c[0] for c in ops.method_calls]
+    assert names.index("remove") < names.index("pattern")
+    assert names.index("pattern") < names.index("groundMotion")
+    assert names.index("groundMotion") < names.index("imposedMotion")
+
+
+def test_unrestrained_node_rejected() -> None:
+    project = _project()
+    project.nodes[0].restraint = (False, True, True, True, True, True)
+    with pytest.raises(ValueError, match="must be restrained in direction 1"):
+        _emit(project)
+
+
+def test_non_dt_path_series_rejected() -> None:
+    project = _project(
+        time_series=[
+            PathTimeSeries(
+                id=1,
+                times=[0.0, 0.1, 0.3],
+                values=[0.0, 1.0, 4.0],
+            )
+        ]
+    )
+    with pytest.raises(ValueError, match="PathTimeSeries with uniform"):
+        _emit(project)
+
+
+def test_vel_tag_collision_rejected() -> None:
+    project = _project()
+    project.time_series.append(PathTimeSeries(id=_IMPOSED_VEL_TS_OFFSET + 7, dt=0.1, values=[0.0]))
+    with pytest.raises(ValueError, match="collides with an existing time series"):
+        _emit(project)
+
+
+def test_direction_beyond_ndf_rejected() -> None:
+    project = _project(
+        ndm=2,
+        ndf=2,
+        nodes=[
+            Node(id=1, coords=(0, 0, 0), restraint=(True, True, False, False, False, False)),
+            Node(
+                id=2,
+                coords=(0, 0, 0),
+                restraint=(False, True, False, False, False, False),
+                mass=(1.0, 0.0, 0.0, 0.0, 0.0, 0.0),
+            ),
+        ],
+        load_patterns=[
+            ImposedSupportMotionPattern(
+                id=7,
+                direction=3,
+                disp_series_id=1,
+                node_ids=[1],
+            )
+        ],
+    )
+    with pytest.raises(ValueError, match="exceeds ndf=2"):
+        _emit(project)