[strohganoff]

Adopt uv for development environments and CI, with committed dependency locking and development tools declared in dependency groups. GitHub Actions now runs the Python 3.9–3.13 matrix directly, replacing Tox.

• Modernize MIT license metadata, add the Python 3.13 classifier, and correct coverage configuration.
• Include Ruff and mypy in development dependencies, target Python 3.9 in Ruff, and clean up stale rule comments and configuration.
• Add a packaging job that builds source and wheel distributions, runs strict Twine checks, and verifies installed-wheel imports and both CLI entry paths outside the checkout.
• Correct stale action imports exposed by the packaging smoke check and update README examples.

Validation: all six CI checks pass on commit 4c26079: tests on Python 3.9–3.13 and the Python 3.13 packaging job. Local builds, strict Twine checks, and clean-wheel smoke checks also passed on Python 3.9.6. Ruff reports 101 existing findings and mypy reports 49 existing errors; neither is enforced by CI.

The published dev extra is replaced by [dependency-groups].dev; contributors now use uv sync --locked and uv run --locked. Broader contributor documentation updates remain separate. Release publishing is unchanged.

Removed two unused mypy ignore comments; the other diagnostics are unchanged and 86 focused tests pass locally. CI for this follow-up is pending.