App-wide configuration cascade for the accordion organism. Resolves in
priority order:
Per-instance Input binding.
provideAccordionConfigAt(...) in a parent component's viewProviders.
provideAccordionConfig(...) at the application root.
Library defaults (this token's factory).
providedIn: 'root' with a default factory means consumers never need to
provide the token explicitly - inject(CNGX_ACCORDION_CONFIG) always
resolves. Consumers who want overrides call provideAccordionConfig(...) in
bootstrapApplication providers (root cascade) or
provideAccordionConfigAt(...) in a component's viewProviders (sub-tree
cascade).