fix(loyalty): register send_notification_email with celery worker

The notifications task module was never imported by the loyalty.tasks
package __init__, so celery's discovery walk loaded the package but
never executed the @shared_task decorator on send_notification_email.
The task was missing from the worker's [tasks] registry, so every
.delay() call resulted in NotRegistered on the worker side — message
ACKed, task silently dropped, no email_logs row written.

Add the import (and update the module docstring / __all__) so the
task is registered alongside the other loyalty background tasks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/modules/loyalty/tasks/__init__.py

@@ -3,17 +3,24 @@
 Loyalty module Celery tasks.
 
 Background tasks for:
+- Transactional notification emails (enrollment, welcome bonus, reward
+  ready, points expiring/expired) — dispatched on-demand by services
 - Point expiration (daily at 02:00)
 - Wallet synchronization (hourly)
 
 Task registration is handled by the module definition in definition.py
-which specifies the task paths and schedules.
+which specifies the task paths and schedules. The imports below must
+mention every task module that defines a @shared_task — otherwise the
+celery worker's task-discovery walk imports the package but never sees
+the decorated function, so calls to .delay() fail with NotRegistered.
 """
 
+from app.modules.loyalty.tasks.notifications import send_notification_email
 from app.modules.loyalty.tasks.point_expiration import expire_points
 from app.modules.loyalty.tasks.wallet_sync import sync_wallet_passes
 
 __all__ = [
     "expire_points",
+    "send_notification_email",
     "sync_wallet_passes",
 ]