Let a coach schedule a line-up to publish itself later

Publish now still works exactly as before (default action), but a coach
can also pick a future date/time -- events.services.lineup.
schedule_lineup_publish sets Lineup.scheduled_publish_at, and a new
periodic task (events.tasks.publish_scheduled_lineups, every 15 minutes)
publishes it once that time arrives via the same publish_lineup used for a
manual publish, so selection/Attendance/notifications all work identically
either way. A pending schedule can be cancelled or published early from the
same screen.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ECGMEwrc2k4D8VQuwjstj9

rosterchief/settings.py

@@ -310,6 +310,9 @@ CELERY_TIMEZONE = TIME_ZONE
 CELERY_BEAT_SCHEDULE = {
     "extend-event-series": {"task": "events.tasks.extend_event_series", "schedule": crontab(hour=3, minute=0)},
     "send-deadline-reminders": {"task": "events.tasks.send_deadline_reminders", "schedule": crontab(hour=7, minute=0)},
+    # Every 15 minutes, not daily like the jobs above -- a coach's scheduled
+    # publish time should take effect close to it, not up to a day late.
+    "publish-scheduled-lineups": {"task": "events.tasks.publish_scheduled_lineups", "schedule": crontab(minute="*/15")},
     "renew-subscriptions": {"task": "billing.tasks.renew_subscriptions", "schedule": crontab(hour=4, minute=0)},
     "send-billing-reminders": {"task": "billing.tasks.send_billing_reminders", "schedule": crontab(hour=5, minute=0)},
     "archive-overdue-clubs": {"task": "billing.tasks.archive_overdue_clubs", "schedule": crontab(hour=6, minute=0)},