- Remove Employee.role CharField — was a display-only label with no
actual permission logic
- 3 migrations: create groups, migrate data, remove field
- Admin: list/filter/fieldset now use groups; added groups_display method
- Serializer: role → groups (SlugRelatedField returning group names)
- Template: get_role_display → groups.first.name
- EmployeePermissionOverride and PermissionGroup remain for fine-grained
per-employee and per-group permission management
lokses