[codex] fix GHCR publishing credentials

[DenisCarriere]

User-facing effect

Main-branch builds can publish the pinax-network/chains-api container package successfully, and the repository no longer reports a failing GitHub Pages deployment for a Pages site that is not enabled.

Root cause

The fork's GITHUB_TOKEN could authenticate to GHCR but received 403 Forbidden when creating the organization-scoped package. The inherited Pages workflow also assumed Pages was configured, while this service now serves its UI directly from Kubernetes.

Fix

• configure repository-scoped GHCR_USERNAME and GHCR_TOKEN Actions secrets from the cluster's established Pinax registry credential;
• use those secrets for container publishing while retaining least-privilege workflow permissions;
• remove the redundant Pages workflow and update maintainer documentation.

Validation

• confirmed the failure was isolated to the GHCR push after both architectures built successfully;
• confirmed the Pages failure was Get Pages site failed because Pages is disabled;
• parsed all remaining workflow YAML files;
• git diff --check.