Delete an EMPTY space

Any member with access to the space may rename it (`name` alone). Sending `kind` (and `teamId` for a team space) re-targets the space's audience — which subject it belongs to, and therefore who can see every page inside it. Those rules are the platform's, enforced by `authkit.AuthorizeRetarget` (docs/platform/subjects-and-containers.md): - the space's creator may re-target their own space; anyone else needs `org.data.audience_manage` (owner/admin) — 403 otherwise - a personal space is never reclassified (400) — move its pages out with `updatePage.workspaceId` instead - only the creator may make a space `personal` (403 otherwise), so a space can't vanish into another person's private area - a `team` target must be a team the caller belongs to (403 otherwise) Re-submitting the current audience is a no-op and needs no permission. Audience changes are written to the platform audit log as `notes.space.audience_changed`.