refactor: 将多个 fmt.Println 日志替换为 log.Printf，以统一日志输出格式并提升可读性

service/beatleader/gen_picture.go

@@ -2,6 +2,7 @@ package beatleader
 
 import (
 	"fmt"
+	"log"
 
 	"git.lxtend.com/qqbot/util"
 )
@@ -16,7 +17,7 @@ func GetBLPicture(qqId string) (outputImgName string) {
 	outputImgPath := util.GenTempFilePath(fmt.Sprintf("beatleader_%s.png", blId))
 	outputImgName = fmt.Sprintf("beatleader_%s.png", blId)
 	if err := util.ScreenshotURL(url, outputImgPath, 1420, 2280, 70, 50, 160, 140, "chartjs"); err != nil {
-		fmt.Println(err)
+		log.Printf("ScreenshotURL error: %v\n", err)
 		return ""
 	}