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.

config/services/celery.py

@@ -38,14 +38,7 @@ app.conf.beat_schedule = {
         'schedule': crontab(hour=2, minute=0),
         'description': 'Runs daily at 02:00 UTC to cleanup notification retention.',
     },
-    'process-scheduled-announcements': {
-        'task': 'apps.communications.tasks.process_scheduled_announcements',
-        'schedule': crontab(minute='*/15'),
-        'description': 'Runs every 15 minutes to dispatch scheduled announcements.',
-    },
 }
 
-EMAIL_TIMEOUT_SECONDS = 10
-
 CELERY_TASK_SOFT_TIME_LIMIT = 20
 CELERY_TASK_TIME_LIMIT = 30