fix: sync test constructor calls with new rpmCache parameter

Add missing nil argument for rpmCache to NewAccountHandler (5 sites)
and NewGatewayService (2 sites) after RPM feature expanded their
signatures.

backend/internal/handler/admin/account_data_handler_test.go

@@ -64,6 +64,7 @@ func setupAccountDataRouter() (*gin.Engine, *stubAdminService) {
 		nil,
 		nil,
 		nil,
+		nil,
 	)
 
 	router.GET("/api/v1/admin/accounts/data", h.ExportData)

backend/internal/handler/admin/account_handler_mixed_channel_test.go

@@ -15,7 +15,7 @@ import (
 func setupAccountMixedChannelRouter(adminSvc *stubAdminService) *gin.Engine {
 	gin.SetMode(gin.TestMode)
 	router := gin.New()
-	accountHandler := NewAccountHandler(adminSvc, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
+	accountHandler := NewAccountHandler(adminSvc, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 	router.POST("/api/v1/admin/accounts/check-mixed-channel", accountHandler.CheckMixedChannel)
 	router.POST("/api/v1/admin/accounts", accountHandler.Create)
 	router.PUT("/api/v1/admin/accounts/:id", accountHandler.Update)

backend/internal/handler/admin/account_handler_passthrough_test.go

@@ -28,6 +28,7 @@ func TestAccountHandler_Create_AnthropicAPIKeyPassthroughExtraForwarded(t *testi
 		nil,
 		nil,
 		nil,
+		nil,
 	)
 
 	router := gin.New()

backend/internal/handler/admin/batch_update_credentials_test.go

@@ -36,7 +36,7 @@ func (f *failingAdminService) UpdateAccount(ctx context.Context, id int64, input
 func setupAccountHandlerWithService(adminSvc service.AdminService) (*gin.Engine, *AccountHandler) {
 	gin.SetMode(gin.TestMode)
 	router := gin.New()
-	handler := NewAccountHandler(adminSvc, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
+	handler := NewAccountHandler(adminSvc, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 	router.POST("/api/v1/admin/accounts/batch-update-credentials", handler.BatchUpdateCredentials)
 	return router, handler
 }