refactor: Replace fmt.Printf with structured logging using logrus in api-server subscriber and invoice services

- Add logrus import to invoice.go, subscriber_crud.go, subscriber_esim.go, and subscriber_lifecycle.go
- Replace fmt.Printf with logrus.WithError and WithField for structured error logging
- Update invoice email notification placeholder to use logrus.Info with invoice_id field
- Replace eSIM provisioning error print with logrus.Warn including subscriber_id field
- Add comment explaining derived

apps/api-server/internal/services/subscriber_esim.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 
 	"github.com/nutcas3/telecom-platform/apps/api-server/internal/models"
+	"github.com/sirupsen/logrus"
 )
 
 // provisionESIMProfile provisions an eSIM profile for the subscriber
@@ -47,7 +48,7 @@ func (s *SubscriberService) provisionESIMProfile(ctx context.Context, subscriber
 
 	// Notify AMF of new subscriber
 	if err := s.amfClient.NotifySubscriberUpdate(ctx, subscriber.IMSI, models.SubscriberStatusActive); err != nil {
-		fmt.Printf("Failed to notify AMF of subscriber activation: %v\n", err)
+		logrus.WithError(err).WithField("imsi", subscriber.IMSI).Warn("Failed to notify AMF of subscriber activation")
 	}
 
 	return nil
@@ -81,12 +82,12 @@ func (s *SubscriberService) deactivateESIMProfile(ctx context.Context, subscribe
 
 	// Terminate all sessions
 	if err := s.terminateSubscriberSessions(ctx, subscriber.IMSI); err != nil {
-		fmt.Printf("Failed to terminate sessions: %v\n", err)
+		logrus.WithError(err).WithField("imsi", subscriber.IMSI).Warn("Failed to terminate sessions")
 	}
 
 	// Notify AMF of subscriber deactivation
 	if err := s.amfClient.NotifySubscriberUpdate(ctx, subscriber.IMSI, models.SubscriberStatusInactive); err != nil {
-		fmt.Printf("Failed to notify AMF of subscriber deactivation: %v\n", err)
+		logrus.WithError(err).WithField("imsi", subscriber.IMSI).Warn("Failed to notify AMF of subscriber deactivation")
 	}
 
 	return nil