fix(example): work-os api callback to reflect documentation

[nthonymiller]

The Workos example states that the callback URL should be http://localhost:3000/api/auth/callback however the example provided an incorrect API implementation.

Changed and moved file from callback.tsx to api/auth.callback.tsx

[LadyBluenotes]

Thanks for catching the callback-path mismatch. This route move was merged later in #5048, and the WorkOS example has since moved to the current AuthKit integration, so this branch is now superseded.

I’ve opened #7790 for the remaining README redirect-URI correction.