Create a role for Student Staff with more management access.

Issue Description:
Create a new role that sits between Student Staff and Program Manager. This role is intended for users who need to manage specific events without receiving all of the responsibilities and permissions associated with a Program Manager.

- The role should be assignable through Admin > Settings > Program Management or something similar
- Administrators should be able to grant the user authority over one or more individual events
- Event permissions should be scoped only to the events assigned to the user

Event Permissions
Users with this role should be able to:
- Create events for the programs that they have been assigned from pre-populated template
- Edit events they are authorized to manage
- Manage RSVPs, attendance, and other event-level administration for only their assigned events
- View only the events they have permission to manage

**This role should not inherit the broader Program Manager permissions.**