Art index reads "Ready." when its build used other settings or an older catalog #176

Follow-up to spec 039 (#122, PR #175), whose Non-Goals ruled settings drift out of scope on 2026-11-03.

What happens. A finished latest art build whose settings_digest differs from the current MTG::Art::Settings.digest, or whose catalog_version is no longer the latest applied refresh's, still reads "Ready." on /admin/catalog's Art index panel and in the art line of catalog:status, as long as its index file exists. After spec 039, a file is judged by being there, not by being current.

Why it matters. An operator who changes art settings (or whose catalog moves on without a rebuild) sees "Ready." while the scanner matches against an index built for other settings or an older catalog.

To decide. Whether drift gets its own panel state and status wording (like 039's "Index file missing"), whether it only adds a fact, and whether the weekly refresh's queued build already makes catalog-version drift short-lived enough to ignore.

Refs: docs/specs/039-art-index-missing-file/spec.md (Non-Goals, Out of Scope), docs/architecture/catalog-operations.md.