Split platform signups, and rework the club table into health

The platform signups chart gets the same stacked new/returning split as the club
one. "First season" is keyed on (club, member), never the member alone: the same
person can be new at one club while renewing at another, and collapsing that would
file their second club's very first signup as a renewal.

The dashboard's club table stops reporting vanity counts. A member total says
nothing you can act on; "no coach", "nothing scheduled", "€ owed" and "no admins"
each name something somebody has to go and fix. Columns are now active members,
unpaid members, money owed, teams (flagging those nobody can pick a squad for),
upcoming events, and admins -- with No season / Dormant badges on the club itself.

Every column is annotated in ONE query, each aggregate in its own subquery. That
is not stylistic: aggregates spanning different joins multiply each other's rows,
so a Sum of orders sitting next to a Count of memberships returns the club's debt
multiplied by its membership count. A test pins €100 against three memberships and
would catch it coming back as €300.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

controlpanel/views.py

@@ -17,7 +17,7 @@ from .services.platform_admins import (
     revoke_platform_access,
     set_platform_access,
 )
-from .services.statistics import club_attention, club_charts, club_statistics, clubs_with_totals, flag_adoption, onboarding_funnel, platform_attention, platform_charts, platform_totals
+from .services.statistics import club_attention, club_charts, club_statistics, clubs_with_health, clubs_with_totals, flag_adoption, onboarding_funnel, platform_attention, platform_charts, platform_totals
 
 Flag = get_waffle_flag_model()
 Switch = get_waffle_switch_model()
@@ -34,7 +34,7 @@ class DashboardView(PlatformStaffRequiredMixin, TemplateView):
             funnel=onboarding_funnel(),
             flags=flag_adoption(),
             charts=platform_charts(),
-            clubs=clubs_with_totals(Club.objects.active()),
+            clubs=clubs_with_health(),
             **kwargs,
         )