After our recent big update to the frontend, I was able to catch a bunch of things I wanted to improve, but weren't really related to that PR. So now I've added the small ones here.

In this PR:

• We resolve an instance where we attempted to write to the headers of a sent response, clogging up my GCP logs
• Removed some missed instances of the old web URL
• Stopped passing dev to templates as we no longer use it
• Standardized and simplified our error rendering utility
• Enabled the frontend to catch errors originating from within ExpressJS

Nothing too big or important in here, but hopefully things that make the repo a little cleaner and better