versioned_docs/ was already tracked but versioned_sidebars/ was never
committed. Docusaurus requires both to render sidebar navigation for
old versions — without the sidebar files, all versioned pages show
no navigation.
Adds sidebar snapshots for user and developer docs:
v0.21.0, v0.22.0, v0.22.1, v0.23.0, v0.23.1, v0.24.0, v0.27.0, v0.28.0
Future versions: CI (docusaurus.yml) runs docs:version on each stable
tag push, which generates both versioned_docs/ and versioned_sidebars/.
The workflow should be updated to commit these files back, or they need
to be added manually after each release.
Impact: Sidebar navigation now appears correctly for all existing
versioned documentation pages.
