Packaged copies

The canonical files live at the repository root (mews-0.1.css) and in dtd/ (mews-0.1.dtd), where SPEC.md and dtd/check_dtd.py reference them. These copies exist so the validator still finds them when it is installed as a wheel, with nothing but the package on disk. tests/test_data.py fails if a copy and its original drift apart.