Lock staff availability so only managers can edit it

Currently any staff member with a login can edit their own appointment availability. It would be useful to have an option to lock availability so that only Owners/Managers can change it.

Use case: employed staff with other operational duties only have specific windows where they're free for bookable appointments, and those windows need to be tied to rota planning and floor cover — not amended by the staff member themselves.

Could be set per role, or per staff member.