feat: carry the catalog forward into the cairn estate

First release under dunn.dev/cairn/pipeline. Carried forward from
dunn.dev/immutable/pipeline at v8.4.0 with full git history and every
release tag intact — the tags below v9 document the design arc that
produced this catalog.

No component was redesigned; this is a home move plus an identity
repoint. The major bump reflects the one breaking change: component
include paths move namespace. Consumers pinning
`dunn.dev/immutable/pipeline/<component>@<tag>` must repoint to
`dunn.dev/cairn/pipeline/<component>@<tag>`.

- Registry image references, component include examples, pipeline and
  release badges, the kickstart/summary clone-URL literals, CI comments,
  and container LABELs repointed to the cairn namespace.
- Estate-identity prose (README, CONTRIBUTING, the builder-image header)
  and the brand SVGs now name the cairn estate.
- README records the carry-forward lineage from immutable/pipeline.

- All dated CHANGELOG entries and annotated-tag release notes below v9.
- Cross-estate references to the still-live immutable basef/instance
  projects and the immutable.dunn.dev estate site.
- The just-recipe (catalog CI) / inline-YAML (component templates) /
  POSIX-sh (release scripts) boundaries.