Type Alias HasMultipleSearchableAttributes<E>

Resolves true when an entity declares more than one Searchable-branded attribute. Consumed by the @Entity decorator constraint so the invalid declaration is a compile error at the class site; metadata validation remains the runtime backstop.

The never guard matters: IsUnion<never> is never, and a never condition is vacuously assignable to true — without the guard every entity with no searchable attribute would trip the constraint.