App-wide configuration cascade for the sidenav family. Resolves in priority
order:
Per-instance Input binding.
provideSidenavConfigAt(...) in a parent component's viewProviders.
provideSidenavConfig(...) 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_SIDENAV_CONFIG) always resolves.
Consumers who want overrides call provideSidenavConfig(...) in
bootstrapApplication providers (root cascade) or provideSidenavConfigAt(...)
in a component's viewProviders (sub-tree cascade).