Background job infrastructure update

Upgraded the infrastructure that runs background jobs (like sending emails and processing chain updates) to a newer, supported version. No visible changes for you.
Started moving our Supabase configuration to their newer, more secure API key system. No visible changes for you.
Added automated checks that every page on the site loads correctly and still looks the way it should, including pages you only see when signed in. This helps us catch problems before they reach you.

The marketing site's header now shows your account menu when you're already signed in, instead of a "Get Started" button as if you weren't.
Fixed a behind-the-scenes error when loading pages with a "request an update" button. The button now remembers that you've recently sent a request without causing an error.