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/migrations/0026_refereesignup.py

@@ -0,0 +1,34 @@
+# Generated by Django 6.0.6 on 2026-08-22 14:32
+
+import django.db.models.deletion
+import uuid
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('events', '0025_remove_lineupunit_lineup_lineupselection_and_more'),
+        ('members', '0006_parentclaim_submitted_by_user'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='RefereeSignup',
+            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)),
+                ('status', models.CharField(choices=[('invited', 'invited'), ('accepted', 'accepted'), ('declined', 'declined')], default='invited', max_length=20, verbose_name='status')),
+                ('responded_at', models.DateTimeField(blank=True, null=True, verbose_name='responded at')),
+                ('event', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='referee_signups', to='events.event', verbose_name='event')),
+                ('member', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='referee_signups', to='members.member', verbose_name='member')),
+            ],
+            options={
+                'verbose_name': 'referee sign-up',
+                'verbose_name_plural': 'referee sign-ups',
+                'ordering': ['event', 'member__last_name', 'member__first_name'],
+                'constraints': [models.UniqueConstraint(fields=('event', 'member'), name='unique_referee_signup_per_event_per_member')],
+            },
+        ),
+    ]