A Bluetooth headset (bluez_output.*) now counts as a hardware clock, so
monitoring on it no longer raises a permanent critical. When pw-top goes quiet
the clock check is WARN, never NA: cannot-measure is a third state. 'Recovered'
is only said for a real recovery (not when the rig closed or the probe went
blind). A health.json left by a gig-log that died uncleanly reads as not
observed instead of aging into a red stale dot on every day it is not running.