What about installation and updating/patching? Or is the intention here to still serve this package of web code, db, etc over the net (via cdn maybe), and then execute locally?
If an app does that...
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.