feat: replace email flows with in-app notifications

Add recipient notification detail and filtering, a queued admin composer, and contextual automatic titles. Retire email delivery, obsolete auth routes, newsletter data, and related templates and settings.

apps/events/migrations/0014_remove_registration_cancellation_email_sent_at_and_more.py

@@ -0,0 +1,26 @@
+# Generated by Django 5.2.5 on 2026-09-26 07:57
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('events', '0013_alter_eventemaillog_kind'),
+    ]
+
+    operations = [
+        migrations.RenameField(
+            model_name='registration',
+            old_name='cancellation_email_sent_at',
+            new_name='cancellation_notification_sent_at',
+        ),
+        migrations.RenameField(
+            model_name='registration',
+            old_name='confirmation_email_sent_at',
+            new_name='confirmation_notification_sent_at',
+        ),
+        migrations.DeleteModel(
+            name='EventEmailLog',
+        ),
+    ]