Generate proactive learner notifications

Attendance warnings and similar nudges, generated in bulk and never duplicated in a day.

1. Open AI → More → Notifications. Review the preview totals.
2. Select Generate for a notification type, such as Attendance Warnings. The message states how many notifications were stored, and the new cards name the learners.
3. Generating the same type again on the same day reports how many were skipped as already sent. Nothing is sent twice.