优化生产日志体积：访问降噪、压缩清理与退款告警节流

跳过轮询/封面等热路径成功请求，按日 gzip 并保留可配天数，退款 max-retry 汇总告警。

backend/internal/logging/logger.go

@@ -39,7 +39,7 @@ func New(cfg config.LogConfig) (*zap.Logger, error) {
 		))
 	}
 	if cfg.EnableFile {
-		writer := newDailyWriter(cfg.Dir, "app", location)
+		writer := newDailyWriter(cfg.Dir, "app", location, cfg.RetainDays)
 		cores = append(cores, zapcore.NewCore(
 			zapcore.NewJSONEncoder(encoderConfig),
 			writer,