The Select all item option should be placed right next to the search button (as indicated in the picture), and preferably not hidden under an action menu.

Already you can select all citations in sections in the Section menu, so it would only make sense to be able to do the same thing on a list level, for instance when you want to tag all citations in the list in one operation.

The preferred workflow would be one click to select all citations, and then having the toolbar appear, the same way it does when you select one citation.