Artifact type catalog gains a cached description lookup

What

• The plugin type-registry reset routine now clears an additional liveReplicas.tooOld set, and splits the old single typeShipsInstructions set into two separate sets: typeCatalogVouch and typeDescriptions.
• A new caching lookup stores per-slug artifact type descriptions in typeDescriptions, keyed by environment and slug, with a positive time-to-live for successful lookups and a shorter backoff before retrying after an error (except a "not_found" error).
• This cache backs artifact publish and resume flows that need a type's title, and only runs when the typeCatalogOn setting is enabled.

Why Caching type descriptions with a TTL avoids repeatedly re-fetching the same artifact type information during publish/resume, while the backoff on errors prevents hammering a failing lookup.