feat(loyalty): Phase 2A — transactional email notifications

Add async email notifications for 5 loyalty lifecycle events, using
the existing messaging module infrastructure (EmailService, EmailLog,
store template overrides).

- New seed script: scripts/seed/seed_email_templates_loyalty.py
  Seeds 5 templates × 4 locales (en/fr/de/lb) = 20 rows. Idempotent.
  Renamed existing script to seed_email_templates_core.py.
- Celery task: loyalty.send_notification_email — async dispatch with
  3 retries and 60s backoff. Opens own DB session.
- Notification service: LoyaltyNotificationService with 5 methods
  that resolve customer/card/program into template variables and
  enqueue via Celery (never blocks request handlers).
- Enrollment: sends loyalty_enrollment + loyalty_welcome_bonus (if
  bonus > 0) after card creation commit.
- Stamps: sends loyalty_reward_ready when stamp target reached.
- Expiration task: sends loyalty_points_expiring 14 days before expiry
  (tracked via new last_expiration_warning_at column to prevent dupes),
  and loyalty_points_expired after points are zeroed.
- Migration loyalty_005: adds last_expiration_warning_at to cards.
- 8 new unit tests for notification service dispatch.
- Fix: rate limiter autouse fixture in integration tests to prevent
  state bleed between tests.

Templates: loyalty_enrollment, loyalty_welcome_bonus,
loyalty_points_expiring, loyalty_points_expired, loyalty_reward_ready.
All support store-level overrides via the existing email template UI.

Birthday + re-engagement emails deferred to future marketing module
(cross-platform: OMS, loyalty, hosting).

342 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/loyalty/tasks/notifications.py

@@ -0,0 +1,72 @@
+# app/modules/loyalty/tasks/notifications.py
+"""
+Async email notification dispatch for loyalty events.
+
+All loyalty notification emails are sent asynchronously via this Celery
+task to avoid blocking request handlers.  The task opens its own DB
+session and calls EmailService.send_template() which handles language
+resolution, store overrides, Jinja2 rendering, and EmailLog creation.
+"""
+
+import logging
+
+from celery import shared_task
+
+logger = logging.getLogger(__name__)
+
+
+@shared_task(
+    name="loyalty.send_notification_email",
+    bind=True,
+    max_retries=3,
+    default_retry_delay=60,
+)
+def send_notification_email(
+    self,
+    template_code: str,
+    to_email: str,
+    to_name: str | None = None,
+    variables: dict | None = None,
+    store_id: int | None = None,
+    customer_id: int | None = None,
+    language: str | None = None,
+):
+    """
+    Send a loyalty notification email asynchronously.
+
+    Args:
+        template_code: Email template code (e.g. 'loyalty_enrollment')
+        to_email: Recipient email address
+        to_name: Recipient display name
+        variables: Template variables dict
+        store_id: Store ID for branding and template overrides
+        customer_id: Customer ID for language resolution
+        language: Explicit language override (otherwise auto-resolved)
+    """
+    from app.core.database import SessionLocal
+    from app.modules.messaging.services.email_service import EmailService
+
+    db = SessionLocal()
+    try:
+        email_service = EmailService(db)
+        email_log = email_service.send_template(
+            template_code=template_code,
+            to_email=to_email,
+            to_name=to_name,
+            language=language,
+            variables=variables or {},
+            store_id=store_id,
+            customer_id=customer_id,
+        )
+        logger.info(
+            f"Loyalty notification sent: {template_code} to {to_email} "
+            f"(log_id={email_log.id if email_log else 'none'})"
+        )
+    except Exception as exc:
+        logger.error(
+            f"Loyalty notification failed: {template_code} to {to_email}: {exc}"
+        )
+        db.rollback()
+        raise self.retry(exc=exc)
+    finally:
+        db.close()