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_screenshot.go

@@ -23,6 +23,9 @@ func (t *GenerateScreenshotTask) Start(ctx context.Context) {
 	scenePath := t.Scene.Path
 
 	videoFile := t.Scene.Files.Primary()
+	if videoFile == nil {
+		return
+	}
 
 	var at float64
 	if t.ScreenshotAt == nil {