Convenience accessor for the accordion configuration cascade. Runs in
injection context; resolves through the priority chain (per-instance Input
-> provideAccordionConfigAt -> provideAccordionConfig -> library
defaults). Equivalent to inject(CNGX_ACCORDION_CONFIG) - the helper exists
so consumers don't import the token directly. Mirrors injectBreadcrumbConfig
in @cngx/ui/breadcrumb.