List, Add, or Remove Publication Collaborators

Manage collaborators (co-creators) for a publication by numeric ID. GET: Returns an ordered list (newest first) of all collaborators. POST: Adds a collaborator by email. Requirements: - Email must correspond to an existing IAMUser account - User must be a member of the publication's workspace with role EDITOR or higher - User must not already be a collaborator and must not be the owner DELETE: Removes a collaborator by email (owner/admin/editor may remove; a user can remove themselves). Permissions: Uses publication/workspace ACL via PublicationPermissionMixin. Error semantics: 404 when publication or user not found / insufficient authority, 400 for validation issues.