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/unit/test_smoke.py

@@ -0,0 +1,17 @@
+"""Smoke tests — verify the package imports and exposes its version."""
+
+from __future__ import annotations
+
+import otko
+
+
+def test_version_exposed() -> None:
+    assert isinstance(otko.__version__, str)
+    assert otko.__version__.count(".") >= 2
+
+
+def test_app_module_importable() -> None:
+    """The bootstrap module must import without instantiating QApplication."""
+    from otko import app
+
+    assert callable(app.run)