Reveals every registered scope on Router.NavigationStart.
Requires provideRouter() (or equivalent) in the host environment.
No-op when no Router is provided so the feature degrades gracefully
in test harnesses or non-routed apps.
Fires before route guards.NavigationStart emits before
CanActivate / CanDeactivate guards run, so a navigation that gets
cancelled by a guard still leaves every scope revealed. Acceptable for
the common pattern (reveal-all on attempted navigation) but surface
the implication when wiring a guard that cancels based on form errors.