Add billing-ending banner, events CRUD, RBIHF import, public API, team photos, and sponsors

A large batch of club-management features built up over one session:

- Club dashboard banner warning admins 1 month before billing ends
- Full Events/EventSeries CRUD (recurrence builder, occurrence lifecycle,
  per-team permissions), with match->game rename and game-specific fields
  (score, competition, live status, external game ID)
- Django-admin competition dropdown, gated per-club by feature flag
- Auto-import of RBIHF fixtures (scrape -> diff -> preview -> confirm),
  with location/opponent dropdowns suggested from existing club data
- Feature-flag-gated Shop/Forms nav sections, reusing the same flag
  machinery for the RBIHF import button
- Team roster now scoped to members active this season or next, sorted and
  grouped by position
- Club sport type (ice hockey / other), shown in the control panel's club
  subtitle
- Per-season team photo upload from the team page
- New public read-only API (Django Ninja) at /api/v1/: news, team rosters,
  upcoming/live/per-team games, and sponsors -- auto-documented via Swagger
  UI, CORS-enabled for a club's own external website
- Club sponsors: admin-only CRUD (logo, URL, active date window) plus a
  date-windowed, optionally randomized API endpoint
- Assorted fixes: NullBooleanField dropdown rendering, cross-club event
  validation timing, searchable-select chip placement, btn-neutral ->
  default button style sweep, calendar-month chart windows

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R1gj3J1QPfP38XWpnpbFpy

club/migrations/0019_sponsor.py

@@ -0,0 +1,36 @@
+# Generated by Django 6.0.6 on 2026-08-06 15:02
+
+import club.models
+import django.core.validators
+import django.db.models.deletion
+import uuid
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('club', '0018_club_sport_type'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Sponsor',
+            fields=[
+                ('created', models.DateTimeField(auto_now_add=True, verbose_name='created')),
+                ('modified', models.DateTimeField(auto_now=True, verbose_name='modified')),
+                ('id', models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, serialize=False)),
+                ('name', models.CharField(max_length=255, verbose_name='name')),
+                ('logo', models.FileField(blank=True, upload_to=club.models.sponsor_logo_path, validators=[django.core.validators.FileExtensionValidator(allowed_extensions=['png', 'jpg', 'jpeg', 'gif', 'webp', 'svg'])], verbose_name='logo')),
+                ('url', models.URLField(blank=True, help_text="The sponsor's own website, if they have one.", verbose_name='URL')),
+                ('start_date', models.DateField(verbose_name='start date')),
+                ('end_date', models.DateField(blank=True, help_text='Leave blank to keep this sponsor active indefinitely once it starts.', null=True, verbose_name='end date')),
+                ('club', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='%(class)ss', to='club.club')),
+            ],
+            options={
+                'verbose_name': 'sponsor',
+                'verbose_name_plural': 'sponsors',
+                'ordering': ['name'],
+            },
+        ),
+    ]