Move admin checks from individual bulk actions to the main handler for
`bulk.rs` and `case_actions.rs`. This consolidates the authorization
logic for these sensitive operations.
Additionally, refine the HTML template to conditionally render bulk
action UI elements and the purge form only when the user is an admin.
This ensures that non-admin users do not see or have access to these
administrative functions.
Update tests to reflect these changes, ensuring that non-admin users are
correctly rejected for these actions and that the UI is properly hidden.
Brummel
1182f4817e