fix: 修复遗漏的测试文件更新和lint错误

- 更新api_contract_test.go以匹配NewAccountHandler新增的tokenCacheInvalidator参数
- 修复errcheck lint错误，显式忽略c.Error()返回值

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/internal/server/api_contract_test.go

@@ -441,7 +441,7 @@ func newContractDeps(t *testing.T) *contractDeps {
 	apiKeyHandler := handler.NewAPIKeyHandler(apiKeyService)
 	usageHandler := handler.NewUsageHandler(usageService, apiKeyService)
 	adminSettingHandler := adminhandler.NewSettingHandler(settingService, nil, nil, nil)
-	adminAccountHandler := adminhandler.NewAccountHandler(adminService, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
+	adminAccountHandler := adminhandler.NewAccountHandler(adminService, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 
 	jwtAuth := func(c *gin.Context) {
 		c.Set(string(middleware.ContextKeyUser), middleware.AuthSubject{