release: htmltools 0.7.0

[schloerke]

Summary

Release prep for htmltools 0.7.0. Sets the CHANGELOG date for the 0.7.0 entry to 2026-05-21. Version in htmltools/__init__.py is already 0.7.0.

Downstream TODOs

.github/workflows/downstream.yaml currently pins each downstream to a feature branch (schloerke/htmltools-105-tagified-types) that absorbs the 0.7.0 type-system changes. Once those downstream PRs land, flip each ref back to main (or delete it to use the repo's default branch):

• posit-dev/py-shiny#2244 — merge, then unpin ref for posit-dev/py-shiny in downstream.yaml
• posit-dev/shinychat#226 — merge, then unpin ref for posit-dev/shinychat in downstream.yaml
• posit-dev/chatlas#311 — merge, then unpin ref for posit-dev/chatlas in downstream.yaml
• posit-dev/brand-yml#115 — merge, then unpin ref for posit-dev/brand-yml in downstream.yaml

Release steps (after merge)

• Tag v0.7.0 on main
• Create GitHub Release named htmltools v0.7.0 — .github/workflows/pytest.yaml auto-publishes to PyPI on release: published when the release name starts with htmltools (use TEST ... for a test.pypi dry run first if desired)

Test plan

• CI green on this branch (pytest + downstream)
• uv build produces a valid wheel/sdist locally