Show battery status

Expose battery info to QML
Display battery level in maui if a battery is present
Add power backends at runtime if they are started after sddm
Yes and no.

you're right there would be multi-greeters but we also have one SocketServer per display.

Daemon 1---n Display   (one per seat/tty)
Display 1....1 SocketServer
SocketServer 1....1 QLocalSocket  (which is our m_connection here)