Add the management app: club-facing UI + real fee-payment tracking

Gives clubs a self-service /manage/ area for members, families, teams,
roles, and season memberships, alongside real fee-payment tracking
(FeePayment, record_payment/mark_as_paid/remaining_balance) so a
membership's paid status reflects actual money received instead of a
single manually-set flag.

management/apps.py

@@ -0,0 +1,5 @@
+from django.apps import AppConfig
+
+
+class ManagementConfig(AppConfig):
+    name = "management"