GHSA-ppwx-5jq7-px2w: Fleet: Device lock PIN can be predicted if lock time is known

Fleet's device lock and wipe PINs were generated using only the current Unix timestamp (the number of seconds since January 1, 1970) without any secret key or random data, making them predictable if an attacker knew approximately when the device was locked. An attacker with physical access to a locked device could theoretically guess the correct 6-digit PIN by trying nearby timestamps, though this would require multiple days of attempts and is limited by the operating system's rate limiting on failed PIN entries.