FetchCertFingerprint read the leaf certificate from a bare insecure TLS
handshake, which CodeQL flagged as go/disabled-certificate-check. The
function intentionally accepts any cert (trust-on-first-use, so the admin
can pin a not-yet-trusted node), so verification cannot be enabled.
Capture the leaf cert inside a VerifyConnection callback instead, matching
the existing pattern in nodeHTTPClientFor that already clears the same
query. Behavior is unchanged.