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

management/templates/management/news_detail.html

@@ -15,7 +15,7 @@
 
 {% block actions %}
     {% if can_edit %}
-        <a class="btn btn-outline btn-neutral gap-2" href="{% url 'management:news_update' news_item.pk %}">{% lucide "pencil" size=16 %} {% trans "Edit" %}</a>
+        <a class="btn btn-outline gap-2" href="{% url 'management:news_update' news_item.pk %}">{% lucide "pencil" size=16 %} {% trans "Edit" %}</a>
         <button class="btn btn-outline btn-error gap-2" type="button" onclick="document.getElementById('delete_news_modal').showModal()">{% lucide "trash-2" size=16 %} {% trans "Delete" %}</button>
     {% endif %}
     {% if can_publish %}
@@ -46,7 +46,7 @@
             <div class="flex items-center justify-between">
                 <h2 class="card-title text-base">{% trans "Photos" %}</h2>
                 {% if can_edit %}
-                    <button class="btn btn-outline btn-neutral btn-sm gap-2" type="button" onclick="document.getElementById('add_photos_modal').showModal()">{% lucide "image-plus" size=14 %} {% trans "Add photos" %}</button>
+                    <button class="btn btn-outline btn-sm gap-2" type="button" onclick="document.getElementById('add_photos_modal').showModal()">{% lucide "image-plus" size=14 %} {% trans "Add photos" %}</button>
                 {% endif %}
             </div>
 
@@ -62,7 +62,7 @@
                                 {% if not photo.is_main %}
                                     <form method="post" action="{% url 'management:news_photo_set_main' news_item.pk photo.pk %}">
                                         {% csrf_token %}
-                                        <button class="btn btn-outline btn-neutral btn-xs gap-1" type="submit">{% lucide "star" size=12 %} {% trans "Set main" %}</button>
+                                        <button class="btn btn-outline btn-xs gap-1" type="submit">{% lucide "star" size=12 %} {% trans "Set main" %}</button>
                                     </form>
                                 {% endif %}
                                 <button class="btn btn-outline btn-error btn-xs gap-1" type="button" onclick="document.getElementById('{{ photo.pk|dom_id:"delete_photo_modal" }}').showModal()">{% lucide "trash-2" size=12 %} {% trans "Delete" %}</button>