Automatic firmware update

We could check the repositories:

For pre-Core watches:

1. Fetch https://raw.githubusercontent.com/pebble-dev/rebble-cohorts/refs/heads/master/config.json
2. Firwmare is at `https://binaries.rebble.io/fw/{hw}/Pebble-{version}-{hw}.pbz`

For Core watches:

https://github.com/coredevices/PebbleOS/releases

And then automatically download / offer user to install