#37 implemented the Sign-_in_ flow, but there wasn't a Sign-_out_ flow as part of that PR (aside from letting the cookie expire... or manually deleting the cookie...), which is obviously not ideal.
This PR implements a basic sign-out flow, along with a very simple user dropdown:

Bringing in a few pruned down components for the `<UserDropdown />` to integrate into the `<NavBar />`.
In addition, this also implements a simple back-end API for `/logout` which just clears the session token.
This just implements a basic sign-in flow, using the new endpoints in #29 :

This brings over several dependencies that are necessary:
- `formik`
- `yep`
Ports over some v1 code to bootstrap it:
- `FormTextField`
- `PasswordField`
- `CoderIcon`
And implements basic sign-in:
Fixes#37Fixes#43
This does not implement it navbar integration (importantly - there is no way to sign out yet, unless you manually delete your `session_token`). I'll do that in the next PR - figured this was big enough to get reviewed.
While starting on the create workspace flow - I noticed some weird CSS issues.
In particular, intermittently, the web UI would render like this:

...and when that happened, there'd be an accompanying error in the console:

The issue is that NextJS is trying to render the page on the server and use the styles - and sometimes the classnames mismatch between server-side and client-side rendering. We actually worked around this in `cdr/m` with a `<SafeHydration />` component and a custom `_document.tsx`
This change ports over both the component and custom `_document.tsx`. I noticed, in addition, I missed the favicons when switching to NextJS, so I brought those over too.