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

events/services/lineup.py

@@ -36,9 +36,15 @@ def publish_lineup(lineup):
     previously unused anywhere. Every selected member becomes SELECTED; every
     other member with an Attendance row for this event who was actually
     available (not out/silent, see UNAVAILABLE_STATUSES) becomes
-    NOT_SELECTED. Notifies only the selected players."""
+    NOT_SELECTED. Notifies only the selected players.
+
+    Clears scheduled_publish_at regardless of whether this run came from a
+    coach tapping Publish directly or from the scheduled sweep (events.tasks.
+    publish_scheduled_lineups) catching a due one -- once published, there's
+    nothing left pending either way."""
     lineup.published_at = timezone.now()
-    lineup.save(update_fields=["published_at"])
+    lineup.scheduled_publish_at = None
+    lineup.save(update_fields=["published_at", "scheduled_publish_at"])
 
     selected_member_ids = set(LineupSelection.objects.filter(lineup=lineup).values_list("member_id", flat=True))
 
@@ -53,6 +59,24 @@ def publish_lineup(lineup):
     return lineup
 
 
+def schedule_lineup_publish(lineup, when):
+    """Sets ``lineup`` to publish itself automatically at ``when`` (an aware
+    datetime in the future) instead of waiting for a manual Publish tap --
+    events.tasks.publish_scheduled_lineups is the periodic sweep that
+    actually calls publish_lineup once that time arrives. Overwrites any
+    previous schedule rather than erroring -- picking a new time is the
+    whole point of letting a coach come back and adjust it."""
+    lineup.scheduled_publish_at = when
+    lineup.save(update_fields=["scheduled_publish_at"])
+    return lineup
+
+
+def cancel_scheduled_publish(lineup):
+    lineup.scheduled_publish_at = None
+    lineup.save(update_fields=["scheduled_publish_at"])
+    return lineup
+
+
 def selected_members_by_position(lineup):
     """Every LineupSelection for ``lineup``, grouped by the member's roster
     position for the lineup's own team/season ("category") -- the read side