CngxTagGroupHost

Public host contract that CngxTagGroup and any future non-component implementer must satisfy. Surfaced through CNGX_TAG_GROUP so child CngxTag directives can read parent state reactively without injecting a concrete parent class.

The field is typed Signal<boolean> (the public parent type), NOT InputSignal<boolean> - test doubles and programmatic groups must be able to satisfy the contract without owning an Angular input(). The CngxTagGroup implementer narrows its InputSignal<boolean> to this public type via direct assignment (readonly semanticList: Signal<boolean> = this.semanticListInput). InputSignal already structurally extends Signal, so no runtime conversion is needed - and .asReadonly() does NOT exist on InputSignal (it lives on WritableSignal only); the type-only narrowing is the canonical bridge.