ci: build docs with the shared docs workflow

[The-Running-Dev]

Replaces the repository's own docs-ci.yml and docs-deploy.yml with the shared docs.yml workflow from GitHub-ActionTemplates (@v0). It builds in the build-agent image, runs on pull requests and on pushes to main, and deploys to GitHub Pages from main only. Repository-specific steps stay in this repository as scripts, passed to the workflow by path.

Depends on GitHub-ActionTemplates#7, released as v0.3.0.

Required check: docs / Build replaces the old docs checks in branch protection and rulesets; the deploy job is docs / Deploy.

Steps

• changelog: docs/docs/engine/CHANGELOG.md with slug: changelog front matter, generated by the shared changelog action. build/ConvertTo-Changelog.ps1 is removed and RELEASE.md §5 updated.
• pre-build: ./build/Test-Documentation.ps1
• node-project: site, scripts check merge, after building src/engine, with browser: true (system Chromium).
• output: artifacts/docs

Also

Comments in ci.yml, host-image.yml and the Dockerfile, agent.md and src/host/README.md name the new workflow.

Site fix

The header nav links had line-height: normal, so their height came from the fallback font's metrics: 15px with DejaVu Sans on Debian and Ubuntu, under the 16px hit-area floor the browser tests assert (Alpine's Open Sans fallback had hidden it). site/src/site.css gives them line-height: 1.5, about 19.7px in any font.

Testing

Built in the build-agent 2.0.0-28 container: changelog (510 entries), pre-build, the docs build and the site's check merge (23/23 browser tests) pass.