feat: Replace interface{} with any type alias for improved code clarity

- Remove omitempty from Plan field in Subscriber model
- Update NotifySubscriberUpdate to use any instead of interface{}
- Update sendDeactivationRequest parameter type from interface{} to any

apps/api-server/internal/models/subscriber.go

@@ -34,7 +34,7 @@ type Subscriber struct {
 	UpdatedAt time.Time      `json:"updated_at"`
 	DeletedAt gorm.DeletedAt `json:"-" gorm:"index"`
 
-	Plan         ServicePlan   `json:"plan,omitempty" gorm:"foreignKey:PlanID"`
+	Plan         ServicePlan   `json:"plan" gorm:"foreignKey:PlanID"`
 	Sessions     []Session     `json:"sessions,omitempty" gorm:"foreignKey:SubscriberID"`
 	UsageRecords []UsageRecord `json:"usage_records,omitempty" gorm:"foreignKey:SubscriberID"`
 }

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

@@ -87,7 +87,7 @@ func (a *AMFClient) TerminateSession(ctx context.Context, imsi models.IMSI, reas
 
 // NotifySubscriberUpdate notifies AMF of subscriber status changes
 func (a *AMFClient) NotifySubscriberUpdate(ctx context.Context, imsi models.IMSI, status models.SubscriberStatus) error {
-	req := map[string]interface{}{
+	req := map[string]any{
 		"imsi":      imsi,
 		"status":    status,
 		"timestamp": time.Now(),

apps/api-server/internal/services/es2_client.go

@@ -308,7 +308,7 @@ func (e *ES2Service) sendActivationRequest(ctx context.Context, req ActivationRe
 	return nil
 }
 
-func (e *ES2Service) sendDeactivationRequest(ctx context.Context, req interface{}) error {
+func (e *ES2Service) sendDeactivationRequest(ctx context.Context, req any) error {
 	jsonData, err := json.Marshal(req)
 	if err != nil {
 		return fmt.Errorf("failed to marshal deactivation request: %w", err)