fix(pollux): check nbf claim in JWT.verify
JWT.verify did not validate the nbf (not before) claim, so JWTs with nbf in the future were incorrectly considered valid. This is a security issue per RFC 7519 Section 4.1.5. Added an explicit nbf check after JWT decode: if nbf is present and the current time is before it, verify() returns false. JWTs without an nbf claim keep the previous behavior (no nbf enforced). This is a sister fix to #489/#550 (which addressed the exp claim). Closes #551 Signed-off-by: Seydi Charyyev <[email protected]>