Target multiple roles in a single campaign

Currently, campaigns can only be targeted to one role at a time —

the role filter in the dashboard allows a single selection, and the

API accepts UIDs rather than roles. Customers with role-based user

segments (e.g. Admin, Employee, Customer, Supplier) need to create

and send a separate campaign for each role, which is repetitive and

hard to manage at scale. Adding multi-role selection so a single

campaign can target a combination of roles (e.g. Admin + Customer)

would let customers reach the right audience in one send.