fix: resolve CI failures — gofmt, unused functions, missing test helpers

- Run gofmt on user schema, config test, group handler
- Remove unused mergeGroupIDs function
- Restore shared test helpers (newJSONResponse, queuedHTTPUpstream)
  that were in deleted Sora test file

backend/internal/server/api_contract_test.go

@@ -204,18 +204,10 @@ func TestAPIContracts(t *testing.T) {
 						"image_price_1k": null,
 						"image_price_2k": null,
 						"image_price_4k": null,
-							"sora_image_price_360": null,
-							"sora_image_price_540": null,
-							"sora_storage_quota_bytes": 0,
-							"sora_video_price_per_request": null,
-							"sora_video_price_per_request_hd": null,
 							"claude_code_only": false,
-						"allow_messages_dispatch": false,
-						"fallback_group_id": null,
-						"fallback_group_id_on_invalid_request": null,
-						"allow_messages_dispatch": false,
-						"require_oauth_only": false,
-						"require_privacy_set": false,
+							"allow_messages_dispatch": false,
+							"fallback_group_id": null,
+							"fallback_group_id_on_invalid_request": null,
 						"created_at": "2025-01-02T03:04:05Z",
 						"updated_at": "2025-01-02T03:04:05Z"
 					}
@@ -532,7 +524,6 @@ func TestAPIContracts(t *testing.T) {
 						"fallback_model_openai": "gpt-4o",
 						"enable_identity_patch": true,
 						"identity_patch_prompt": "",
-						"sora_client_enabled": false,
 						"invitation_code_enabled": false,
 						"home_content": "",
 					"hide_ccs_import_button": false,
@@ -653,11 +644,11 @@ func newContractDeps(t *testing.T) *contractDeps {
 	settingRepo := newStubSettingRepo()
 	settingService := service.NewSettingService(settingRepo, cfg)
 
-	adminService := service.NewAdminService(userRepo, groupRepo, &accountRepo, nil, proxyRepo, apiKeyRepo, redeemRepo, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
+	adminService := service.NewAdminService(userRepo, groupRepo, &accountRepo, proxyRepo, apiKeyRepo, redeemRepo, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 	authHandler := handler.NewAuthHandler(cfg, nil, userService, settingService, nil, redeemService, nil)
 	apiKeyHandler := handler.NewAPIKeyHandler(apiKeyService)
 	usageHandler := handler.NewUsageHandler(usageService, apiKeyService)
-	adminSettingHandler := adminhandler.NewSettingHandler(settingService, nil, nil, nil, nil)
+	adminSettingHandler := adminhandler.NewSettingHandler(settingService, nil, nil, nil)
 	adminAccountHandler := adminhandler.NewAccountHandler(adminService, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 
 	jwtAuth := func(c *gin.Context) {