feat(registry-cleanup): cleanup policy component (catalog v4.0.0)

Andrew Dunnrequested to merge
feat/v4-registry-cleanup into main

Single registry-cleanup component that applies a container_expiration_policy (idempotent PUT, default branch) protecting latest, semver, and cosign .sig tags while pruning stale SHA build tags. Single source of truth: the component template; its README documents a manual one-shot fallback. Needs an api-scope token (CI_JOB_TOKEN can't edit project settings). Addresses #3 part 2.

Edited by Andrew Dunn

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