Add referee assignment/eligibility system, team bulk-add, member Groups, and referee management dashboard with PDF export

Builds the referee workflow end to end: club-defined RefereeLevel/RefereeProfile
eligibility tied to teams, EventReferee assignment (member or external, with
fee/km payment tracking), an admin dashboard with KPI tiles, date-grouped game
tiles and range filters, and a downloadable payment form PDF modeled on the
club's existing paper document (using Club.legal_name when set). Also lands
team roster bulk-add, member mass-upload with family linking, and the
members.Group model, developed alongside this work.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

teams/services.py

@@ -0,0 +1,17 @@
+from django.utils import timezone
+
+from club.models import ClubMembership, Season
+from members.models import Member
+
+
+def eligible_roster_members(club):
+    """Members eligible to be added to a team's roster or staff: active (paid) for
+    the club this season or next, regardless of which season's roster/staff list is
+    currently being edited (the team page's season switcher can point at either)."""
+    today = timezone.localdate()
+    eligible_seasons = [season for season in (Season.covering(club, today), Season.next_after(club, today)) if season is not None]
+    return Member.objects.filter(
+        member_of__club=club,
+        member_of__season__in=eligible_seasons,
+        member_of__status=ClubMembership.StatusChoices.ACTIVE,
+    ).distinct()