Introduce a `validate_display_order` method to ensure a default value of 0 for `display_order`. Extend testing infrastructure with fixtures and unit tests for `EventMedia` to validate properties, metadata, and default behaviors.
Introduce a `validate_display_order` method to ensure a default value of 0 for `display_order`. Extend testing infrastructure with fixtures and unit tests for `EventMedia` to validate properties, metadata, and default behaviors.