Backend: add autoSignup field to OidcConfig, ClickHouse schema, repository, and admin controller. Gate OIDC login when auto-signup is disabled and user is not pre-created (returns 403). Frontend: add OIDC admin page with full CRUD (save/test/delete), role-gated Admin nav link parsed from JWT, and matching design system styles. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>