Remarkably, I stumbled upon Tellico, a program that met all these requirements and then some, after six months of on-and-off searching.
Developed by Robby Stephenson as a hobby, Tellico is described as a collection manager for KDE, a common desktop environment for Linux. Ubuntu Linux uses the Gnome desktop, but can install and run KDE applications with no problem. To install Tellico, simply choose it in the Synaptic Package Manager.
I don’t think Tellico has ever been mentioned in a newspaper before. This is a milestone!