Re-publish under nakata-truthcheck on PyPI.

Changed

• mypy override now ignores missing stubs for numpy (prevents spurious import-not-found on CI without the [nli] extra).
• [dev] extras include pytest-cov>=4.1 so the CI pytest --cov=truthcheck step succeeds.

Added

• SECURITY.md, CONTRIBUTING.md, CHANGELOG.md, GitHub PR + issue templates (cluster parity).
• .github/workflows/release.yml for tag-driven build + PyPI publish.

No public-API change.

Install: pip install nakata-truthcheck==0.1.1