artifact: core/events/src/main/kotlin/com/correx/core/events/serialization/Serialization.kt
purpose: Register SteeringNoteAddedEvent in the eventModule polymorphic block via subclass(SteeringNoteAddedEvent::class) to prevent silent runtime deserialization failure.
depends_on: task-004
non_goals: Modifying any other serialization blocks, adding new serializers
done_when: ./gradlew check passes — specifically the serialization round-trip test for SteeringNoteAddedEvent