Retire the client-side changelog registry refresh

[cotti]

Why

Phase 3 of elastic/docs-eng-team#688, stacked on #3738. With the scrubber Lambda as the sole producer of the public bundle manifests and the shallow per-tree maps (#3738), the client-side registry refresh is the last remaining writer in the retired multi-writer model. Keeping it would let a stale private manifest linger (nothing consumes it anymore) and would keep upload logs claiming registry responsibility the CLI no longer has.

Note

Restacked 2026-08-06: this PR previously sat on #3741 (registry reconcile/verify CLI), which was closed after review — the per-product registry cutover tooling went with it. It now stacks directly on #3738, whose rework scopes group reconciliation to the bundle tree and adds the shallow folder→token maps.

What

changelog upload now writes YAML objects only: the post-upload refresh block, RegistryBuilder, and the private-manifest write path are gone. The registry materializes from the S3 events the upload already emits. The amend end-to-end test now drives RegistryReconciler (the production path) for its registry step, and the upload tests assert that no registry.json is ever PUT.

Old binaries in the wild keep writing private manifests — harmless: bundle registry-key events only schedule a group reconcile and are never copied to the public bucket.

Important

Do not merge until the Phase 2 cutover checkpoint passes (scrubber Lambda deployed with #3738, queue drained, DLQ empty, and a spot-check that public bundle/{product}/registry.json manifests carry the reconciler's producer field — see elastic/docs-eng-team#688). Releasing this before the Lambda owns the public registry would leave registries permanently stale.

After this releases, the now-dead private registry.json objects can be deleted (operational step, no code): their ObjectRemoved events only schedule redundant reconciles.

Part of elastic/docs-eng-team#688 (Phase 3).

[cotti]

Restacked: #3741 was closed with the per-product cutover tooling, so this now sits directly on #3738 (rebased onto its reworked branch — shallow per-tree maps, group reconcile scoped to the bundle tree). Same single commit, no content changes beyond the rebase; 849/849 tests green on the new chain. Now part of stack #3800 (#3738 ← this ← #3794).