Add a team attendance KPI panel and no-show check-in tracking

Team pages now show, for the selected season: overall attendance rate,
best/worst attenders, players who missed the last 2 practices, and
no-shows (an affirmative RSVP checked in as absent). No-shows need a
real distinction the RSVP status alone can't make, so Attendance gains
a separate showed_up tri-state field, usable today via Django admin --
a full check-in screen is future work for the coaches app.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R1gj3J1QPfP38XWpnpbFpy

events/services/__init__.py

@@ -1,4 +1,12 @@
-from .attendance import effective_members, sync_event_attendances
+from .attendance import (
+    effective_members,
+    player_attendance_rankings,
+    players_who_missed_recent_practices,
+    record_check_in,
+    sync_event_attendances,
+    team_attendance_rate,
+    team_no_shows,
+)
 from .recurrence import (
     apply_template,
     cancel_occurrence,
@@ -17,6 +25,11 @@ __all__ = [
     "generate_occurrences",
     "horizon",
     "occurrence_datetimes",
+    "player_attendance_rankings",
+    "players_who_missed_recent_practices",
     "propagate_series",
+    "record_check_in",
     "sync_event_attendances",
+    "team_attendance_rate",
+    "team_no_shows",
 ]