It grew, as projects do, out of its original simple use case and now it needs to be usable in scenarios where network access won't be available for most of the work day, which means I need to rebuild it --in whatever time I can manage to devote to it, dev not being my primary or even secondary responsibility-- to deal with that and better handle the functionality we tacked on later.
After a review of my options, which unfortunately doesn't seem to include writing a native application (for reasons I still may be able to work around), I'm thinking that my simplest option is to just write a single page of JS that writes HTML to the DOM directly and works with data entirely locally, synchronizing it with a server API (.NET) when available. Basically, just a client application written in JS. No special frameworks, no complicated toolchains. Even that is a pain in the ass because the web world hasn't quite worked out how to store local data in a non-stupid way.