Smoother GitHub setup and team invitations

Small fixes make connecting a repository and bringing teammates into Flex more dependable.

Finish connecting GitHub

We fixed the redirect flow used when connecting GitHub, so you can return to the workspace and continue setting up your repository. This update also fixes email-based team invitations.

Repository access for previews

Preview Git operations now use a credential proxy. It handles repository authentication on behalf of the preview, improving how previews obtain the access they need when working with source code.