Entity struct for one customize — a customization of an EXISTING component. The rules inside
decide which world it targets: color/variant/size/… ⇒ a styled component, part ⇒ a
headless one. Never both.
Built by the customize entity in MishkaChelekom.Kit.Dsl; consumed by
MishkaChelekom.Kit.Transformers.Generate and the MishkaChelekom.Kit.Verifiers.*.