When sessionwatch.Watcher.Update rejects a deadline (pre-epoch, too far
in the future, or past the clock-skew tolerance) it silently zeroes the
status recorder, leaving the UI with no "expires in" row and no
indication of why. Publish a SystemEvent_ERROR on the AUTHENTICATION
channel so the rejection appears in the UI event feed and the user
knows re-login may be required.
Also add Debugf log lines in armTimerLocked so that warning and
final-warning timer fire-times are visible in logs without having to
add instrumentation after the fact.
https://claude.ai/code/session_01Y3bQoNgcVjTD4zDTvv7a8u
c0b00eed46