Correct handler class name and route name separator in routing page

[arhimede]

The routing page documented a class that no longer exists and a route name that throws when used.

• PageHandler was renamed to GetPageViewHandler in release 1.2.0, but both the prose and the code sample still used the old name.
• The code sample iterated $moduleName and wrapped the handler in an array; the current src/Page/src/RoutesDelegator.php iterates $prefix and passes the handler unwrapped. The sample now matches the source verbatim.
• The route name was given as page.about. The separator is ::, so url('page.about') throws — request-lifecycle.md already had it right and the two pages contradicted each other.
• The claim that every module loops over config routes was wrong: only Page does. App registers a single static / route, which is now shown.