Let referee levels inherit from a lower level instead of relying on ordering alone

RefereeLevel.inherits_from chains levels together so a higher tier is
automatically eligible for everything a linked lower tier covers,
transitively, without hand-duplicating teams onto every level. Kept
the ordering field (still drives display order) but eligibility
everywhere (RefereeProfile.eligible_teams, events.services.referees,
the team detail page's eligible-referees list) now reads through
RefereeLevel.eligible_team_ids, which walks the inherits_from chain.
clean() rejects a loop, including an indirect one.

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

events/tests.py

@@ -1205,6 +1205,18 @@ class RefereeServiceTests(EventsTestBase):
 
         self.assertEqual(set(eligible_referees(game)), set())
 
+    def test_eligible_referees_includes_a_higher_level_via_inheritance(self):
+        # self.level ("Regional") qualifies for self.team; a referee holding a
+        # higher level that inherits from Regional (without self.team added
+        # directly) must still show up -- see RefereeLevel.eligible_team_ids.
+        national = RefereeLevel.objects.create(club=self.club, name="National", inherits_from=self.level)
+        national_referee = Member.objects.create(first_name="Nat", last_name="Ional")
+        self.make_eligible_profile(national_referee, level=national)
+
+        game = self.make_home_game()
+
+        self.assertIn(national_referee, set(eligible_referees(game)))
+
     def test_eligible_referees_ignores_an_expired_profile(self):
         expired_referee = Member.objects.create(first_name="Ex", last_name="Pired")
         RefereeProfile.objects.create(member=expired_referee, level=self.level, valid_until=timezone.localdate() - timedelta(days=1))