This goes together with the solution to "a way to export/import the database". Export/import is a usability dead end. What we need is syncing. There should be

This goes together with the solution to "a way to export/import the database". Export/import is a usability dead end. What we need is syncing. There should be a serverless way to sync data. On a LAN there are several ways to do it: databases, files. With possibly untrusted devices (phones) on different networks (PC on home LAN, phone on the operator network) the solution is... I don't know.