Support file-less scenes. Add scene split, merge and reassign file (#3006)

* Reassign scene file functionality
* Implement scene create
* Add scene create UI
* Add sceneMerge backend support
* Add merge scene to UI
* Populate split create with scene details
* Add merge button to duplicate checker
* Handle file-less scenes in marker preview generate
* Make unique file name for file-less scene exports
* Add o-counter to scene update input
* Hide rescan for file-less scenes
* Generate heatmap if no speed set on file
* Fix count in scene/image queries

internal/manager/task_generate_preview.go

@@ -73,6 +73,10 @@ func (t GeneratePreviewTask) generateWebp(videoChecksum string) error {
 }
 
 func (t GeneratePreviewTask) required() bool {
+	if t.Scene.Path == "" {
+		return false
+	}
+
 	sceneHash := t.Scene.GetHash(t.fileNamingAlgorithm)
 	videoExists := t.doesVideoPreviewExist(sceneHash)
 	imageExists := !t.ImagePreview || t.doesImagePreviewExist(sceneHash)