The item detail page already listens for the app-wide `library-changed`
event and navigates away; the playlist and collection detail pages did
not, so switching libraries left them showing stale content with no way
back to the list.
- playlist/_id.vue: route to /bookshelf/playlists on library change
- collection/_id.vue: route to /bookshelf/collections unless the new
library is the collection's own library
