Component-scoped configuration cascade for the toc organism. Pass any
combination of feature factories in a parent component's viewProviders
array.
Unlike provideTocConfig (root-only), provideTocConfigAt injects the
parent injector's CNGX_TOC_CONFIG value (resolves through the priority
chain) and deep-merges the supplied features on top. Descendant toc
instances see the merged config; sibling sub-trees keep the inherited value.