feat: Users API, ownership transfer and removal of the legacy role string

features/invitations.feature

@@ -1,5 +1,6 @@
 Feature: A verified user can invite another person by email, and the users list shows users and open invites
   Superseded in part by roles_permissions_enforcement: the owner and admin 403 clauses now answer 403 "missing_permission" with the header X-Missing-Permission, decided by the caller's role permissions. An Admin can now invite and write sites, and a role without the needed permission is refused on routes that were open to every verified user.
+  Superseded in part by roles_permissions_users_api: the invite body gains an optional role_id (absent or 0 means the Writer role), the invite response and the invite items of the users list carry role (a RoleRef, keys {id, name, built_in, locked}), the key lists of those shapes gain role, and the inviter must cover the role (403 escalation, role_locked, invalid_role). A user created by accepting an invite takes the role of the invite instead of Admin.
 
   As a member of the shared RenewCMS workspace
   I want to invite someone by email and see who has an account or a pending invite