docs(fern): publish ordered version snapshots

[pimlock]

Summary

Publish each tagged release as both Latest and an immutable vX.Y.Z docs entry from the same source commit. Keep Latest and Dev at the top, followed by versioned entries newest first. Current release jobs request no availability badges; the optional badge mechanism remains available for future use.

Related Issue

No issue required: this is a focused correction to documentation publishing and version selector presentation.

Changes

• Switch Release Tag's single docs sync to the stable channel, which creates the versioned snapshot and updates Latest in one publish.
• Sort versioned selector entries by parsed version regardless of publish order.
• Leave availability unset in Release Dev, Release Tag, and the source Fern config. Keep the optional availability input in the sync workflow and preserve badges on entries that are not being updated.
• Clear the existing Dev Beta badge on its next Dev sync; the tagged release creates unbadged Latest and versioned entries.
• Document snapshot and selector behavior in the Fern and build architecture docs.

Testing

• mise run test:docs-website passes (26 tests).
• mise run docs passes (0 errors, 3 warnings).
• mise run pre-commit passes.
• mise run test passes.
• mise run ci passed before the badge follow-ups; the changed Python tests, docs, and lint checks were rerun afterward.
• E2E tests added or updated; not applicable to docs publishing configuration.

Checklist

• Follows Conventional Commits.
• Commits are signed off for DCO.
• Architecture docs updated.

[github-actions]

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