feat(schema): retain and publish ontology archives

What does this MR do and why?

Retain each schema version's ontology and publish it before migration so it remains available after upgrades. Query serving, readiness, and promotion stay unchanged.

Related Issues

Relates to #184 (closed). First split of !2433 (closed).

Testing

1,100 unit tests and 81 Docker integration tests passed, including NATS restart persistence. Clippy, formatting, and archive-retention CLI checks passed.

Performance Analysis

• This merge request does not introduce any performance regression. If a performance regression is expected, explain why.

Agent context

Archive contract. Reuses the shared extractor.

Local logs: /tmp/orbit-archive-split-all-unit.log, /tmp/orbit-archive-split-regression.log, /tmp/orbit-archive-split-clippy.log, /tmp/orbit-archive-split-cli.log.

Docs lint: pre-existing line-length violation at docs/design-documents/indexing/sdlc_indexing.md:244.