Move docs build into the Checks workflow

[cristianrgreco]

Summary

• Run the strict docs build as a Docs job in the Checks workflow instead of a separate Docs workflow, so it reports as Checks / Docs alongside the other checks. docs.yml is removed.
• Remove paths-ignore from Checks so the docs job runs on docs-only changes. changed-modules.mjs already ignores README.md, docs/** and mkdocs.yml, so lint, compile, smoke tests and tests still skip for those changes; only Detect packages to check (~5s) newly runs.
• Checks complete now needs docs and runs with if: always(), so a failed docs build fails it on docs-only changes too. Previously it was skipped when no packages changed.
• Drop the Netlify Python version comment from the docs job.

Verification

• npm run format — no fixes applied
• npm run lint — no fixes applied
• printf 'docs/index.md\nmkdocs.yml\nREADME.md\n' | node .github/scripts/changed-modules.mjs — prints [], confirming the package jobs skip for docs-only changes
• Parsed checks.yml as YAML and confirmed the job list and the end job's needs

The workflow itself is exercised by this PR's own run. Because checks.yml counts as an all-packages change, this PR runs the full matrix.

Not breaking

CI-only change; no published package code, public API or docs content is touched. The main ruleset has no required status checks, so renaming Docs / Build docs to Checks / Docs does not affect merging.