docs(release): backport release-line docs refresh

[dc-tec]

Summary

Backports #458 to release-0.2 so future 0.2.x patch releases can refresh the existing 0.2.x docs snapshot instead of publishing stale release-line docs.

This keeps the 0.2.x versioned docs aligned with the plugin behavior shipped in 0.2.1, keeps release-line labels in the docs version dropdown, and adds the release-branch CI guard that requires matching versioned-docs updates when source docs change on release-* branches.

Related Issues

Backports #458.
Related to the 0.2.1 release follow-up.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor (code improvement/cleanup)
• CI, release, or build tooling
• Other maintenance

Risk and Compatibility

Low runtime risk; this only changes docs, docs tooling, and CI routing on the release-0.2 branch. Public docs paths remain stable. The refresh command intentionally uses the checked-out branch docs, so 0.2.x snapshots can be refreshed from release-0.2 without pulling in main or future 0.3.x docs.

Verification

• node --check website/scripts/snapshot-version.mjs && node --check website/scripts/refresh-version.mjs
• ./bin/actionlint .github/workflows/*.yml
• npm --prefix website run typecheck
• temp-tree execution of website/scripts/refresh-version.mjs 0.2.0, verifying versions.json order stays 0.2.0,0.1.0
• npm --prefix website run build
• npm --prefix website run test:e2e
• git diff --check origin/release-0.2...HEAD
• pre-push make lint-ci

Reviewer Notes

This PR also fixes the refresh script behavior for the transient state where 0.2.0 is temporarily removed from versions.json while the snapshot is rebuilt. The Docusaurus version labels are now only applied for versions currently present in versions.json.

Checklist

• My code follows the project style guide.
• I have performed a self-review of my own code.
• I have added or updated tests, or explained why tests are not needed.
• I have updated documentation, or explained why docs are not needed.
• I have updated generated artifacts, or confirmed none are affected.
• I have checked that this change does not log or expose secrets, tokens, credentials, keys, or raw Secret data.
• I have run the relevant local checks, or documented why they were not run.
• Any dependent changes have been merged, published, or clearly called out.