Implement auth component for Svelte

[mpscholten]

The thin-backend-react/auth-ui.tsx module should be ported to Svelte to thin-backend-svelte, so that we can provide in-app login in Svelte apps as well 👍

[TheUltDev]

Mitosis may be a good solution this issue, and #25 #35 #42 as well.
Not affiliated with them, but I would like React Native support.
All frameworks could possibly be supported easily this way.

[mpscholten]

Thanks for pointing out. We've actually looked into Mitosis already :) It's working well for simple components, but more complex functionality still requires manual adjustments.

There's an expo template here btw: https://github.com/digitallyinduced/ihp-backend-expo-starter It might be a bit oudated, but it's definitly possible to run Thin with React Native already.