Incorrect <title> value set for external pattern-library pages

[lyzadanger]

For consuming applications that add their own pattern library pages (routes), the HTML <title> element is getting set incorrectly when routing.

The relevant useEffect hook in /src/pattern-library/components/PatternLibraryApp is looking at the wrong set of routes (this array only contains routes defined by the pattern library source):

  // Update document title when `wouter` path changes.
  useEffect(() => {
    const activeRoute = routes.find(({ route }) => route === pathname);
    document.title = `${
      activeRoute?.title ?? 'Page not found'
    }: Hypothesis Component Library`;
  }, [pathname, routes]);

The net result is that page titles on pages added by applications get set to:

Page not found: Hypothesis Component Library