rendering data as graphs: WARDEN_GITHUB_VERIFIER_SECRET env variable not set

Guide doesn't mention it, code doesn't mention. Unable to build server without it
> No WARDEN_GITHUB_VERIFIER_SECRET environmental variable found.
> Your sessions are likely being stored insecurely.

Start at the server build entry point and the setup guide, then search the repository for WARDEN_GITHUB_VERIFIER_SECRET and the quoted warning. Confirm the required setup path by reproducing the build failure; done means the guide and relevant server documentation consistently explain the variable and how to proceed.

Written by the indexing model from the issue text.