Ruff autofix removed pre-existing F401 unused imports across adapters,
context, compiler, extractor, scheduler, web, and main. Also reordered
models.py so its SQLAlchemy imports sit at the top of the file
(E402 was triggered by the inline `utcnow` helper definition).
Added a [dependency-groups] dev block (pytest, pytest-cov, ruff) so the
zero-check test gauntlet — which runs `pytest --cov --cov-report=term-missing`
— can resolve its plugins without a manual `uv pip install pytest-cov`.
