Let eligible referees self-serve sign-up for games needing one

Creating (or re-teaming) a home game for a club-managed team now auto-
invites every eligible referee (teams.RefereeProfile) via a new
RefereeSignup model, notifying them the same way news/events already do.
They see it as its own distinct row on the mobile Calendar (own accent
colour) and can accept or decline right there -- accepting routes through
the existing capacity-checked assign_referee (assigned_by=None marks it
self-service), so it lands as a real EventReferee row with no separate sync
step. The desktop referee-management screen and event detail page both
surface pending invites and flag self-signed-up referees distinctly from
admin assignments.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ECGMEwrc2k4D8VQuwjstj9

events/signals.py

@@ -21,6 +21,7 @@ from django.utils.translation import gettext_lazy as _
 from club.models import ClubMembership
 from events.models import Event, EventSeries
 from events.services import sync_event_attendances
+from events.services.referees import sync_referee_invites
 from members.models import Group, GroupMembership
 from teams.models import Team, TeamMembership
 
@@ -50,6 +51,7 @@ def validate_groups_same_club(sender, instance, action, reverse, pk_set, **kwarg
 @receiver(post_save, sender=Event)
 def sync_on_event_save(sender, instance, **kwargs):
     sync_event_attendances(instance)
+    sync_referee_invites(instance)
 
 
 @receiver(m2m_changed, sender=Event.teams.through)
@@ -68,6 +70,18 @@ def sync_on_audience_change(sender, instance, action, reverse, model, pk_set, **
             sync_event_attendances(event)
 
 
+@receiver(m2m_changed, sender=Event.teams.through)
+def sync_referee_invites_on_teams_change(sender, instance, action, reverse, **kwargs):
+    # Referee eligibility only depends on `teams` (needs_referee_management),
+    # not groups/invited/excluded_members -- a separate, narrower receiver
+    # rather than folding into sync_on_audience_change above, which is about
+    # attendance specifically. reverse (team.scheduled_events.add(...)) isn't
+    # a used path -- see validate_teams_same_club's own comment.
+    if action not in M2M_SYNC_ACTIONS or reverse or not isinstance(instance, Event):
+        return
+    sync_referee_invites(instance)
+
+
 @receiver(post_save, sender=TeamMembership)
 @receiver(post_delete, sender=TeamMembership)
 def sync_on_roster_change(sender, instance, **kwargs):