* refactor: replace datetime.now with timezone.now
* refactor: migrate model fields to use timezone.now as default
* refactor: replace datetime.today with timezone.now
datetime.datetime.today() is equivalent to datetime.datetime.now(); both
return a naive datetime with the current local time.
* refactor: rephrase datetime.now(tz) as timezone.now().astimezone(tz)
This is effectively the same, but is less likely to encourage accidental
use of naive datetimes.
* refactor: revert datetime.today() change to old migrations
* refactor: change a missed datetime.now to timezone.now
* chore: renumber timezone_now migration
* chore: renumber migrations
