runbooks: record that the private twin is archived

The plan said the private ops/runbooks still needed retiring. It did not: the steward's Gitea token carries write:organization and can archive repos, which I had wrongly believed it could not (that belief came from a different operation, an org-user rename, needing a different scope). ops/runbooks is now archived — it held the same five files as this repository and was behind it, so nothing was lost, and archived rather than deleted keeps it inspectable and reversible.

cloudron-server-migration.md

@@ -10,6 +10,10 @@
 > anything marked "to do" below, and the mail architecture (see the note further down).
 >
 > **Where the live knowledge lives now:** the `cloudron-ops` skill for operational procedure, and
+
+> **The private twin `ops/runbooks` was ARCHIVED by the steward on 2026-11-02.** It held nothing this
+> repository lacks (same five files, this one ahead) and is now read-only, so there is a single
+> maintained copy. Archived rather than deleted: reversible, and the history stays inspectable.
 > `co-op/docs/infrastructure.md` for the member-facing description. Those two are maintained; this
 > file is not.