fix(backend): sprint 4 post-review — relative paths + dead branch removal

- test_engagement_lifecycle.py, test_simulations_techniques.py: replace hardcoded
  absolute paths with Path(__file__).parent.parent / migrations/... (portable)
- simulation_workflow.py: remove dead branch in transition() — the IN_PROGRESS
  hook was unreachable since _ALLOWED_TRANSITIONS only targets review_required/done

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/tests/test_simulations_techniques.py

@@ -405,10 +405,11 @@ def test_migration_0003_techniques_not_null_after_upgrade() -> None:
         import alembic.op as _op_module
         _op_module._proxy = ops  # type: ignore[attr-defined]
 
-        spec = importlib.util.spec_from_file_location(
-            "mig_0003",
-            "/home/user/Documents/01_Projects/mimic/.claude/worktrees/sprint-4-ui-polish/backend/migrations/versions/0003_simulation_techniques_array.py",
+        _mig_path = (
+            pathlib.Path(__file__).parent.parent
+            / "migrations" / "versions" / "0003_simulation_techniques_array.py"
         )
+        spec = importlib.util.spec_from_file_location("mig_0003", _mig_path)
         assert spec is not None and spec.loader is not None
         mig = importlib.util.module_from_spec(spec)
         spec.loader.exec_module(mig)  # type: ignore[union-attr]