Per-vault membership (/admin/knowledge-base/:vault/members) — who can open a
vault, and what they can do in it.
Only a vault owner reaches this page. For a personal vault that is its
creator; for an organisation vault it is anyone holding
knowledge_base.manage_system_vaults.
The implicit owner of a personal vault has no row here and cannot be removed, which is what stops a vault ending up with nobody able to administer it.