Set the aria-current token [cngxTabLink] publishes while active. Default 'page'.
Use 'true' for a section nav whose links stay active across a whole
subtree: the active link is then the current section, and page
would tell AT it is the page being viewed. Scope it to one nav with
provideTabsConfigAt in that component's viewProviders rather than
setting it app-wide, unless every nav in the app is section-shaped.
Per-link [ariaCurrent] still wins.