Docs already said any module or app could publish bread.command.<app>.<verb>,
but command is reserved so both unsourced bread-emit and sourced App emit
rejected the whole namespace. Keep command unclaimable as an app id; accept
bread.command.<known-app>.<verb> (and let an app command another known app).
Also ship bread-emit and bread-module-host, and give udev enumerate the same
classification fields as a live add so boot-time devices are not all unknown.
