This may be an outdated question, but can I pair an 800 device in LR mode using hubitat's built-in web server (just like mesh pairing) or do I need to use a phone and app?
LR requires SmartStart, so the app is necessary to scan the QR code.
I recommend using Jeff's SmartStart tool for managing SmartStart -- lots of good info about LR pairing here:
Technically... you can use my custom app to manually add something to SS without the mobile app, if they give you the full key with the QR code and you don't mind typing it all in.
For sure is easier to just scan the code with the mobile app.
For laughs, I just pointed my Samsung phone at a device QR code, it asked me if I wanted to add it to SmartThings! Needless to say I backed out of that. 