- Add types for scope, action, resource_permission, permission_set
- Implement get_permissions/1 for all 4 sets (own_data, read_only, normal_user, admin)
- Implement valid_permission_set?/1 for string and atom validation
- Implement permission_set_name_to_atom/1 with error handling
Use Ash.Changeset.force_change_attribute to set is_system_role in tests
since it's no longer settable via public API. Remove unused nil clause
from error_message helper.
Use Enum.reject for nil field case to explicitly filter errors
without field. Update test to use :is_system_role field since
validation error includes field.
