pub fn install(app: &mut App, plan: &PagePlan)Expand description
Install the page registry, in-memory history, the reserved-signal seeds,
and the navigation systems onto a built app. Called once at boot when
plan.multipage is set.
The PagePlan goes in as a resource alongside the routing itself,
because a from-source run reloads pages from the files it names. A compiled
app has no files to reload and installs through install_routing.