BREAKING CHANGE: lib_utils.security removed entirely. All JWT-related
public names (encode_jwt, decode_jwt, decode_jwt_unverified,
decode_jwt_to_model, create_technical_auth_header, AuthJwtModel,
JWTValidationError, InvalidJWTError, ExpiredJWTError,
JWTClaimsValidationError) moved to the new lib-auth-guard library.
Consumers must depend on lib-auth-guard >= 0.1.0 and rewrite
imports `from lib_utils.security import ...` to
`from lib_auth_guard import ...`. Public signatures are preserved 1:1.

- src/lib_utils/security/ deleted
- tests/security/ deleted
- python-jose[cryptography] dropped from project dependencies
- types-python-jose dropped from dev dependencies
- README and CHANGELOG updated with migration notes