perfsprint 18→0：strconv.Itoa/FormatInt/FormatUint/FormatBool 替代 fmt.Sprintf、无动词 fmt.Errorf→errors.New、纯字符串拼接。全部语义等价（已核对 diff）。修正 fixer 遗留的 import 问题（引入 goimports 统一整理）。

Result: {"status":"keep","total_issues":56,"golint_canonicalheader":8,"golint_errname":1,"golint_errorlint":12,"golint_forcetypeassert":3,"golint_gosec":0,"golint_intrange":3,"golint_modernize":5,"golint_nilnil":3,"golint_perfsprint":0,"golint_prealloc":3,"golint_recvcheck":7,"golint_usestdlibvars":3,"golint_wastedassign":7,"golint_total":55,"eslint_problems":1,"eslint_errors":0,"eslint_warnings":1,"tsc_errors":0,"measure_s":47}

internal/apps/upload/handler/routers.go

@@ -204,7 +204,7 @@ func DownloadFile(c *gin.Context) {
 		}
 	}
 
-	c.Header("Content-Disposition", fmt.Sprintf("attachment; filename*=UTF-8''%s", url.PathEscape(fileName)))
+	c.Header("Content-Disposition", "attachment; filename*=UTF-8''"+url.PathEscape(fileName))
 	filesrv.ServeUpload(c, upload)
 }