Release v0.18.1

[schloerke]

Summary

Cuts chatlas 0.18.1, picking up the two PRs merged since 0.18.0:

• fix: annotate .tagify() return types per htmltools Tagified contract #311 (Improvements) — Content.tagify() implementations now annotate as htmltools.Tagified and fully tagify their output, complying with htmltools 0.7.0's tightened Tagifiable contract.
• Export ContentPDF from chatlas.types #312 (Bug fixes) — ContentPDF is now exported from chatlas.types.

Commits

1. docs(changelog): add #311 Tagified contract entry under UNRELEASED — backfills the missing changelog entry from fix: annotate .tagify() return types per htmltools Tagified contract #311.
2. Release v0.18.1 — renames ## [UNRELEASED] → ## [0.18.1] - 2026-05-21.

Release steps after merge

Per .github/workflows/release.yml (fires on release: published when the tag starts with v):

1. Tag the merge commit v0.18.1.
2. Publish a GitHub Release pointing at that tag.
3. release.yml runs make check-types / make check-format / uv build, then trusted-publishes to PyPI.

Version itself is computed by hatch-vcs from the tag; no _version.py to bump.