Cut 19.0.1 and bump package version in pyproject.toml, uv.lock, and
CITATION.cff.

Patch: update PyPI short description metadata from #189.

Changelog:
- Add 19.0.1 section dated 2026-09-16 with #189 entry.

Docs: none needed here. This release documents an already-landed
metadata change.

Testing:
- make check -> pass: 1622 passed, 52 skipped; Rust tests 156 passed,
  1 ignored; lint, format, pyright, and clippy pass.
- uv lock --check -> pass.
- uv run mkdocs build --strict -> pass; upstream Material for MkDocs
  emitted its MkDocs 2.0 warning.