tests: Add E2E tests

[helmturner]

Due to a minor miscommunication about route paths, I broke the site on our first feature deployment. This really underscores the need for E2E testing in our pipeline to catch and prevent exactly this sort of thing.

A primary goal of our E2E testing will be to interact with the site just as the user would, so it's important we avoid interacting with elements programmatically whenever possible.