Support CORS in Repl Auth script (https://replit.com/public/js/repl-auth-v2.js)

Currently, the auth script does not support CORS, which means that it breaks with a security plugin like helmet.

Adding CORS support would allow us to use security features like COEP and SRI hashes.

I was attempting to add login support to my web page when the script refused to load and Fastify threw an error. (Yes, I was using fastify-helmet, but it’s a wrapper around helmet anyway.)