test(07.3-01): Wave 0 Nyquist scaffold — 9 xfail stubs for ES256 + remember_me

- Create test_auth_es256.py with 9 xfail(strict=True) stubs: ES256-01..05, RM-01..03, CFG-01
- Add es256_keys(autouse) fixture using cryptography P-256 keygen + monkeypatch with raising=False
- Extend test_settings_has_jwt_config to assert refresh_token_expire_hours==16 + jwt key fields

backend/tests/test_task1_models_config.py

@@ -29,6 +29,10 @@ def test_settings_has_jwt_config():
     assert settings.access_token_expire_minutes == 15
     assert hasattr(settings, "refresh_token_expire_days")
     assert settings.refresh_token_expire_days == 30
+    assert hasattr(settings, "refresh_token_expire_hours")
+    assert settings.refresh_token_expire_hours == 16
+    assert hasattr(settings, "jwt_private_key")
+    assert hasattr(settings, "jwt_public_key")
 
 
 def test_settings_has_smtp_config():