Add group/club-wide event audiences and a Resend email backend

Events can now target members.Group audiences alongside teams, or go
club_wide (every ACTIVE ClubMembership member for the event's season)
instead of specific teams/groups -- the two are mutually exclusive,
enforced in EventForm/EventSeriesForm.clean() since an M2M can't be
validated via a DB CheckConstraint or Event.clean() (no PK yet). Attendance
sync (events/signals.py) now reacts to GroupMembership and ClubMembership
changes the same way it already did for TeamMembership. Authorization:
club.services.access.groups_manageable_by mirrors teams_managed_by (all
groups for an ADMIN, else only the ones the user belongs to -- Group has no
manager/owner concept); a non-admin needs at least one managed team or
belonged-to group to create/edit an event, club_wide stays admin-only, and
EventManagerRequiredMixin gained a get_groups() hook so a non-admin who
creates a group-only event isn't immediately locked out of managing it.

Also adds rosterchief.mail.ResendEmailBackend, an HTTP-API-based Django
email backend for Resend (resend.com) using the existing `requests`
dependency -- no new SDK. Opt in via DJANGO_EMAIL_BACKEND and RESEND_API_KEY;
every Django-sent email (allauth's password reset included) follows
whichever EMAIL_BACKEND is configured, so this covers all of them for free.
Resend's own SMTP relay remains a valid code-free alternative, documented
alongside it in .env.production.example.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

management/templates/management/_nav_items.html

@@ -25,11 +25,11 @@
 <li class="menu-title">{% trans "Teams" %}</li>
 <li><a class="{% if nav == 'team_list' %}menu-active{% endif %}" href="{% url 'management:team_list' %}">{% lucide "shirt" size=16 %} {% trans "Teams" %}</a></li>
 <li><a class="{% if nav == 'position_list' %}menu-active{% endif %}" href="{% url 'management:position_list' %}">{% lucide "tags" size=16 %} {% trans "Positions" %}</a></li>
-<li><a class="{% if nav == 'referee_list' %}menu-active{% endif %}" href="{% url 'management:referee_list' %}">{% lucide "flag" size=16 %} {% trans "Referees" %}</a></li>
 {% if is_club_admin %}
-    <li><a class="{% if nav == 'referee_management' %}menu-active{% endif %}" href="{% url 'management:referee_management' %}">{% lucide "calendar-check" size=16 %} {% trans "Referee management" %}</a></li>
     <li><a class="{% if nav == 'referee_level_list' %}menu-active{% endif %}" href="{% url 'management:referee_level_list' %}">{% lucide "badge-check" size=16 %} {% trans "Referee levels" %}</a></li>
+    <li><a class="{% if nav == 'referee_management' %}menu-active{% endif %}" href="{% url 'management:referee_management' %}">{% lucide "calendar-check" size=16 %} {% trans "Referee management" %}</a></li>
 {% endif %}
+<li><a class="{% if nav == 'referee_list' %}menu-active{% endif %}" href="{% url 'management:referee_list' %}">{% lucide "flag" size=16 %} {% trans "Referees" %}</a></li>
 
 <li class="menu-title">{% trans "News" %}</li>
 <li><a class="{% if nav == 'news_list' %}menu-active{% endif %}" href="{% url 'management:news_list' %}">{% lucide "newspaper" size=16 %} {% trans "News" %}</a></li>

management/templates/management/event_detail.html

@@ -65,6 +65,16 @@
                         <dt class="text-sm opacity-70">{% trans "Teams" %}</dt>
                         <dd>{% for team in event.teams.all %}{{ team.name }}{% if not forloop.last %}, {% endif %}{% empty %}—{% endfor %}</dd>
                     </div>
+                    <div class="flex items-center justify-between py-2">
+                        <dt class="text-sm opacity-70">{% trans "Groups" %}</dt>
+                        <dd>{% for group in event.groups.all %}{{ group.name }}{% if not forloop.last %}, {% endif %}{% empty %}—{% endfor %}</dd>
+                    </div>
+                    {% if event.club_wide %}
+                        <div class="flex items-center justify-between py-2">
+                            <dt class="text-sm opacity-70">{% trans "Audience" %}</dt>
+                            <dd><span class="badge badge-primary">{% trans "Whole club" %}</span></dd>
+                        </div>
+                    {% endif %}
                 </dl>
             </div>
         </div>

management/templates/management/event_form.html

@@ -24,6 +24,12 @@
                 <h3 class="text-lg font-semibold mb-3">{% trans "Audience" %}</h3>
                 <div class="grid grid-cols-1 md:grid-cols-3 gap-4">
                     {% form_field form.teams %}
+                    {% form_field form.groups %}
+                    {% if "club_wide" in form.fields %}
+                        {% form_field form.club_wide %}
+                    {% endif %}
+                </div>
+                <div class="grid grid-cols-1 md:grid-cols-2 gap-4 mt-4">
                     {% form_field form.invited_members %}
                     {% form_field form.excluded_members %}
                 </div>

management/templates/management/event_series_form.html

@@ -41,6 +41,12 @@
                 <h3 class="text-lg font-semibold mb-3">{% trans "Audience" %}</h3>
                 <div class="grid grid-cols-1 md:grid-cols-3 gap-4">
                     {% form_field form.teams %}
+                    {% form_field form.groups %}
+                    {% if "club_wide" in form.fields %}
+                        {% form_field form.club_wide %}
+                    {% endif %}
+                </div>
+                <div class="grid grid-cols-1 md:grid-cols-2 gap-4 mt-4">
                     {% form_field form.invited_members %}
                     {% form_field form.excluded_members %}
                 </div>