Hi !
I discovered today another project opensource, a web file explorer without database too, do you know it ?
filegator.io
It do what FilesGallery don't : multi-select, move files, and user management and vice versa, the front interface is not pretty, no thumbnail of images, effects, tree navigation...
So i mixed thoses apps with 2 websites root alias : the first with FileGator for edit mode and the second with yours for view/access mode...
Maybe some ideas you can find in this project to help you to implement theses features ?
Best regards,