Implement Bearer token validation using jsonwebtoken with JWKS caching
and automatic key rotation handling. AuthState fetches keys from the
configured OIDC provider's jwks_uri at startup and refreshes on unknown
kid. Axum middleware (require_auth) protects write routes, injecting
AuthenticatedUser into request extensions. The auth_check admin endpoint
now performs real JWT validation when oauth2 is configured.
Includes architecture plan for the full publish API with RBAC at
docs/ai/plans/2026-04-09-publish-api-oidc.md.
