Link the academy notebooks from the platform, and put their re-run in the release procedure

Parent

Spec: #2454 — Document and teach the OEKG REST API. Derived from WF-15 decisions D16 and D17.

What to build

The notebooks become reachable from the platform, and the chore that keeps them true gets an owner.

They are frozen snapshots protected by nothing mechanical — the code→doc pinning test for them was specified, costed and declined. A dated banner plus a line on the release procedure is therefore their entire defence, so that line has to actually exist, in the document releases are actually run from.

Acceptance criteria

• Both tutorial URLs are added to the platform's external tutorial URL map, beside the existing academy tutorial links.
• The OEKG API documentation links to both notebooks.
• RELEASE_PROCEDURE.md gains a step in its numbered release list: after the production deploy, re-run both academy notebooks against production and update their dated banner to the released version.
• The step names the academy repository, since the files being re-run and re-committed live there.
• Changelog entry.

Blocked by

• #2463 and #2464 — the two notebooks — both URLs are needed, and there is nothing to re-run until both exist.