Build the platform metrics dashboard

The dashboard leads with the numbers that are supposed to be zero, because a
dashboard of healthy counts is one nobody opens:

- Clubs with no season covering today. Seasons scope memberships, rosters and
  events, so such a club cannot take a signup or schedule a match -- and it fails
  silently, nothing errors, it is just inert.
- Dormant clubs: nothing on the calendar for 30 days. Churn signal.
- Admins pending MFA. RequireMFAMiddleware redirects them to enrolment, so they
  are locked out of their own club until they act: a support queue, not a stat.
- Outstanding money across every club.

Then the shape of the business: an onboarding funnel (clubs → with members → with
a team → with events, which separates working clubs from shells), feature-flag
adoption per club, and two charts -- signups and revenue per month.

Charts use chart.js, self-hosted rather than pulled from a CDN, for the same
reason as the fonts: no third-party in the render path. Two things the browser
taught me: the canvas needs a height-bounded wrapper (with maintainAspectRatio
off it sizes to its parent, and a parent with no height grew it to 3489px), and
chart.js cannot read daisyUI's CSS variables, so the charts re-render on a
data-theme change or keep the light palette in dark mode.

The month series is zero-filled: a chart that skips empty months draws a smooth
line straight over a month in which nothing happened.

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_statistics, clubs_with_totals, platform_totals
+from .services.statistics import club_statistics, clubs_with_totals, flag_adoption, onboarding_funnel, platform_attention, platform_charts, platform_totals
 
 Flag = get_waffle_flag_model()
 Switch = get_waffle_switch_model()
@@ -30,6 +30,10 @@ class DashboardView(PlatformStaffRequiredMixin, TemplateView):
         return super().get_context_data(
             nav="dashboard",
             totals=platform_totals(),
+            attention=platform_attention(),
+            funnel=onboarding_funnel(),
+            flags=flag_adoption(),
+            charts=platform_charts(),
             clubs=clubs_with_totals(Club.objects.active()),
             **kwargs,
         )