Split club signups into new members and renewals

A "New members" card sits beside Renewal, and the signups chart becomes a stacked
bar: bar height stays "signups this month" while the split shows where they came
from.

New means "first-ever season at this club", not "signed up recently". A member who
lapsed for a year and came back is a renewal, and counting them as new would
flatter every recovery into growth. It is also per club, not per platform: someone
who plays for another club is still new here.

The split resolves each member's earliest season once up front rather than asking
per row, so the chart costs two queries instead of one per membership.

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

controlpanel/tests.py

@@ -30,11 +30,13 @@ from .services.statistics import (
     dormant_clubs,
     fee_aging,
     flag_adoption,
+    new_members,
     onboarding_funnel,
     platform_attention,
     platform_charts,
     platform_totals,
     renewal_rate,
+    signup_split,
     teams_without_a_manager,
     unrostered_members,
 )
@@ -866,3 +868,65 @@ class ClubDetailMetricsTests(ControlPanelTestBase):
         response = self.client.get(reverse("controlpanel:club_detail", args=[self.club.pk]))
 
         self.assertContains(response, "cannot take a signup")
+
+
+class NewMemberTests(TestCase):
+    def setUp(self):
+        self.club = Club.objects.create(name="Ajax United")
+        self.today = timezone.localdate()
+        self.previous = Season.objects.create(club=self.club, start_date=self.today - datetime.timedelta(days=400), end_date=self.today - datetime.timedelta(days=40))
+        self.season = Season.objects.create(club=self.club, start_date=self.today - datetime.timedelta(days=30), end_date=self.today + datetime.timedelta(days=300))
+        self.veteran = Member.objects.create(first_name="Ada", last_name="Lovelace")
+        self.rookie = Member.objects.create(first_name="Bob", last_name="Bobson")
+
+    def membership(self, member, season, signed_up_at=None):
+        return ClubMembership.objects.create(club=self.club, season=season, member=member, status=ClubMembership.StatusChoices.ACTIVE, signed_up_at=signed_up_at)
+
+    def test_only_first_timers_count_as_new(self):
+        self.membership(self.veteran, self.previous)
+        self.membership(self.veteran, self.season)
+        self.membership(self.rookie, self.season)
+
+        new = new_members(self.club, self.season)
+
+        self.assertIn(self.rookie, new)
+        self.assertNotIn(self.veteran, new)
+
+    def test_a_member_returning_after_a_gap_is_not_new(self):
+        # They skipped a season and came back. Counting that as growth would flatter every
+        # recovery; they are a renewal.
+        self.membership(self.veteran, self.previous)
+        gap = Season.objects.create(club=self.club, start_date=self.today - datetime.timedelta(days=39), end_date=self.today - datetime.timedelta(days=31))  # noqa: F841
+        self.membership(self.veteran, self.season)
+
+        self.assertNotIn(self.veteran, new_members(self.club, self.season))
+
+    def test_a_member_of_another_club_is_new_here(self):
+        # "New" is per club, not per platform.
+        other = Club.objects.create(name="Feyenoord")
+        other_season = Season.objects.create(club=other, start_date=self.today - datetime.timedelta(days=400), end_date=self.today - datetime.timedelta(days=40))
+        ClubMembership.objects.create(club=other, season=other_season, member=self.rookie)
+        self.membership(self.rookie, self.season)
+
+        self.assertIn(self.rookie, new_members(self.club, self.season))
+
+    def test_a_club_with_no_season_has_no_new_members(self):
+        self.assertEqual(new_members(self.club, None).count(), 0)
+
+    def test_signups_are_split_by_month_into_new_and_returning(self):
+        self.membership(self.veteran, self.previous, signed_up_at=self.today - datetime.timedelta(days=200))
+        self.membership(self.veteran, self.season, signed_up_at=self.today)
+        self.membership(self.rookie, self.season, signed_up_at=self.today)
+
+        this_month = signup_split(self.club)[-1]
+
+        self.assertEqual(this_month["new"], 1)  # the rookie
+        self.assertEqual(this_month["returning"], 1)  # the veteran renewing
+
+    def test_a_first_ever_signup_counts_as_new_in_its_own_month(self):
+        self.membership(self.veteran, self.previous, signed_up_at=self.today - datetime.timedelta(days=200))
+
+        series = signup_split(self.club)
+
+        self.assertEqual(sum(month["new"] for month in series), 1)
+        self.assertEqual(sum(month["returning"] for month in series), 0)