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/models.py

@@ -124,6 +124,13 @@ class Attendance(UUIDModel):
     event = models.ForeignKey(Event, on_delete=models.CASCADE, related_name="attendances", verbose_name=_("event"))
     member = models.ForeignKey(Member, on_delete=models.CASCADE, related_name="attendances", verbose_name=_("member"))
     status = models.CharField(_("status"), max_length=20, choices=AttendanceStatus.choices, default=AttendanceStatus.NO_RESPONSE)
+    showed_up = models.BooleanField(
+        _("showed up"),
+        null=True,
+        blank=True,
+        default=None,
+        help_text=_("Recorded by a check-in, separate from the RSVP status above. Blank means no check-in has been recorded yet."),
+    )
     note = models.TextField(_("note"), blank=True)
 
     class Meta: