feat: add system task runner (#5680)

model/midjourney.go

@@ -101,6 +101,19 @@ func GetAllUnFinishTasks() []*Midjourney {
 	return tasks
 }
 
+// HasUnfinishedMidjourneyTasks reports whether at least one Midjourney task is
+// still in progress. It is a cheap existence check (LIMIT 1) used to decide
+// whether the midjourney_poll system task needs to run; when no task is pending
+// the scheduler skips creating a row entirely.
+func HasUnfinishedMidjourneyTasks() bool {
+	var id int
+	err := DB.Model(&Midjourney{}).
+		Where("progress != ?", "100%").
+		Limit(1).
+		Pluck("id", &id).Error
+	return err == nil && id != 0
+}
+
 func GetByOnlyMJId(mjId string) *Midjourney {
 	var mj *Midjourney
 	var err error