- Add last_confirm_sent_at to subscriptions, with a migration for
existing databases. registerSubscription now sends at most one
confirmation email per 10 minutes per subscription, so a page-refresh
or client retry storm can't spam an inbox. The cooldown resets when
the address changes or a tombstoned row is reactivated (fresh key),
so genuinely new addresses always get an email immediately.
- Restore getCronExpression to the documented daily (17:00 UTC) and
weekly (Monday 17:00 UTC) schedules with the 6-field cron syntax the
cron package expects, fixing the pre-existing reschedule tests that the
'run every minute' testing hack had broken.
- Add confirm-email-cooldown.test.ts covering first send, refresh storms,
frequency changes, email changes, reactivation, and the 10-minute constant.
(cherry picked from commit 051c1e88fb)
