fix(release): record scan observation time at nanosecond precision

Trivy stamps DownloadedAt with nanosecond precision while the evidence
recorded observedAt in whole seconds, so when both landed in the same
second the truncated observation sorted "before" the download and the
evidence verifier rejected the ordering. Record observedAt at the same
precision so program order is preserved in the timestamps.

Co-authored-by: Cursor <cursoragent@cursor.com>