This may work if the developer is a possible client too like in this case. But I feel that’s the exception.

Do what the clients want and not what developers, designers or management want.

Seems so. Checked the sources and there’s no upload/download. And testing it I can confirm the network tab in the dev tools is silent. Everything work local side. Probably with some additional work this could be converted to a PWA (Progressive Web App) and work completely offline.

The good place