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/services/card_service.py

@@ -624,6 +624,23 @@ class CardService:
 
         wallet_service.create_wallet_objects(db, card)
 
+        # Send notification emails (async via Celery)
+        try:
+            from app.modules.loyalty.services.notification_service import (
+                notification_service,
+            )
+
+            notification_service.send_enrollment_confirmation(db, card)
+            if program.welcome_bonus_points > 0:
+                notification_service.send_welcome_bonus(
+                    db, card, program.welcome_bonus_points
+                )
+        except Exception:
+            logger.warning(
+                f"Failed to queue enrollment notification for card {card.id}",
+                exc_info=True,
+            )
+
         logger.info(
             f"Enrolled customer {customer_id} in merchant {merchant_id} loyalty program "
             f"(card: {card.card_number}, bonus: {program.welcome_bonus_points} pts)"