fix(lint): resolve remaining ruff violations in PR #11037

F401: Remove unused datetime imports (UTC, datetime) from
  features/steps/invariant_model_steps.py and robot/helper_invariant_model.py
  (auto-populated timestamps removed explicit values per B2 fix).

RUF022: Sort InvariantModel alphabetically in __all__ within
  src/cleveragents/infrastructure/database/__init__.py.

All CI lint violations resolved. Closes review blockers from #11037.

features/steps/invariant_model_steps.py

@@ -7,7 +7,6 @@ querying by is_active, and schema validation.
 from __future__ import annotations
 
 import uuid
-from datetime import UTC, datetime
 
 from behave import given, then, when  # type: ignore[import-untyped]
 from behave.runner import Context  # type: ignore[import-untyped]

robot/helper_invariant_model.py

@@ -4,7 +4,6 @@ from __future__ import annotations
 
 import sys
 import uuid
-from datetime import UTC, datetime
 from pathlib import Path
 
 # Ensure src is importable when run from workspace root

src/cleveragents/infrastructure/database/__init__.py

@@ -98,8 +98,8 @@ __all__ = [
     "DuplicateSkillError",
     "DuplicateToolError",
     "DuplicateValidationAttachmentError",
-    "InvariantModel",
     "InvalidToolTypeError",
+    "InvariantModel",
     "LifecycleActionModel",
     "LifecyclePlanModel",
     "LifecyclePlanRepository",