How many users hold this role

The blast radius of a role edit, as one number.

Exists so the confirmation dialog can say WHO it affects instead of "all holders". The frontend cannot compute this: the only role-assignment field it receives is Z_Users.idrole (8 rows on the test clone), while the real answer comes mostly from Z_UserRoles (210) — counting client-side would understate a 142-user role as 1 and make the warning worse than useless.