feat(settings): add default subscriptions for new users

- add default subscriptions to admin settings

- auto-assign subscriptions on register and admin user creation

- add validation/tests and align settings UI with subscription selector patterns

backend/cmd/jwtgen/main.go

@@ -33,7 +33,7 @@ func main() {
 	}()
 
 	userRepo := repository.NewUserRepository(client, sqlDB)
-	authService := service.NewAuthService(userRepo, nil, nil, cfg, nil, nil, nil, nil, nil)
+	authService := service.NewAuthService(userRepo, nil, nil, cfg, nil, nil, nil, nil, nil, nil)
 
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()