Show an Arch-specific message if no app backends are available
Arch developers have repeatedly expressed a preference for Arch users to use the command line to manage software, rather than Discover. For this reason, they deliberately package Discover in such a way that you will have to go out of your way to figure out how to install an app backend. Unfortunately, this means that Discover looks broken if you install it with its default set of dependencies, because it won't be able to find any apps. Novice Arch users don't understand that this is a deliberate packaging choice in Arch, and instead blame Discover. To alleviate this, we have introduced an error page that has become ever mode specific over time about what exactly the problem is. Despite this, novice Arch users remain confused about it. And the text we show today is not really correct, as it implies that the issue is caused by a bug in Arch's packaging. But it is *not* a bug; Arch packagers package Discover this way deliberately, because they don't want Arch users to use Discover to get apps. They consider this to be an expert level feature that you shouldn't use unless you know what you're doing, which inherently conflicts with the UX that we want to offer in Discover. Accordingly, for Arch users, let's show an Arch-specific message that explains what's going on in clear and precise language, and offers an actionable path forward.