Add Authentik OIDC auth to Grafana
Wire Grafana's generic OAuth against auth.klab.sh (KLab Auth), gated to the grafana-admins/grafana-users groups with admins mapped to the Admin role and everyone else to Viewer. Local admin login stays enabled as a break-glass fallback. Client id/secret placeholders go in example.env; real values are set on the server only.
Co-Authored-By: Claude Sonnet 5 noreply@anthropic.com