A one-shot alarm can now ring on a chosen date, and a repeating alarm
can be paused for a range of days. Both are local dates: the date is a
floor and the pause a hole in the occurrence sequence, so DST and zone
changes resolve as for any other alarm. A missed date behaves like a
missed one-shot, and each clears itself once it can no longer change a
candidate. Picking a repeat day clears the date, as in Google Clock;
"skip next" stays the quick version of a pause.
The editor uses the M3 date and date-range pickers, which offer no past
day. The list, the next-alarm widget and the self-check read the
resolver, so they follow. The schema goes to v4 with a migration, and
the backup format to v2, which still imports v1 files. SET_ALARM no
longer re-uses an alarm that carries a date or a pause.
Fixes#21
