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.

rosterchief/urls.py

@@ -24,6 +24,7 @@ urlpatterns = [
     path("admin/", admin.site.urls),
     path("accounts/", include("allauth.urls")),
     path("controlpanel/", include("controlpanel.urls")),
+    path("manage/", include("management.urls")),
     # "/" resolves per tenant: a club subdomain lands on the club, the base domain
     # hands off to the control panel. This is why LOGIN_REDIRECT_URL can stay "/".
     path("", root, name="root"),