Third round of review fixes for the silence-after setting.
A backstop that fires while the clock is still behind the ring's start
now closes the ring instead of re-arming in a loop until the wall clock
catches up. A clock change re-measures a ring in progress before it
reschedules: a clock moved back re-arms the backstop at most one window
from the moved clock, and one moved forward past the window closes the
ring.
The engine now owns the alarm setting's write. setAlarmSilenceAfter
stores it and re-measures the ring under one lock and without
cancellation, so a write can no longer land without the re-measure.
A snooze the resolver drops takes its "Snoozed until" notification with
it. SNOOZE_GRACE is derived from the default window, and the silence-after
picker moves to ui/settings, since it is not a per-alarm override.
Refs #17
makiolaj
4cb4b6b6eb