Migrate backend and add authentication

[newswim]

Right now we have one endpoint called cosmos and we pass a query from the frontend. A better pattern would be to create a separate endpoint for each visualization (that way we get more separate of concerns).

The one outlier will be the dynamic chart at the top. For that, @Matt343 has been working on a query builder that we'll likely use on the backend, by sending filter params to the endpoint.

See:

• https://next-auth.js.org/tutorials/securing-pages-and-api-routes
• https://github.com/orgs/vercel/discussions/1833