96e9df7: feat: add SSO support to authentication provider — AuthPlugin interface with authorize, handleCallback, refreshTokens, and getUserProfile methods, GessoTokenSet and GessoUser types with roles/groups/metadata, createCustomAuthProvider for redirect-based auth flows, and normalized error handling with AuthErrorCode
a76f4bb: feat: add runtime behavior to authentication provider — createSessionManager for session lifecycle, normalizeAuthError for error mapping, createCommerceAuthPlugin and createCmsAuthPlugin adapters, lifecycle hooks wiring in getAuth, and validatePlugin utility