Bind installed starter documentation links to the Registryctl release

[jeremi]

Outcome

An installed Registryctl starter links to documentation for the same released command and schema contract, so an older binary never sends an adopter to mutable current-version instructions.

Context

PR #598 installs the bounded HTTP starter from released Registryctl bytes. Its README currently uses current documentation URLs. This is safe for the 1.0 candidate but can drift after later releases.

Definition of Done

• Starter documentation URLs are materialized from the installed release version.
• Development builds have an explicit unreleased-docs fallback.
• Tests prove released starters never contain mutable current-docs links.
• Archive routes and checksums remain compatible with the released tutorial bundle.

Non-goals

• Embedding the full documentation site in Registryctl.
• Runtime documentation discovery.
• Backporting pre-1.0 starter behavior.