- backend/config.py: add refresh_token_expire_hours=16, jwt_private_key, jwt_public_key - backend/services/auth.py: add import base64; all 4 JWT sites use ES256 with inline PEM decode; zero HS256/secret_key references - backend/tests/test_auth_es256.py: promote ES256-01..03 + CFG-01 tests from xfail to passing