When the configured Ethernet interface holds a DHCP-assigned IPv4 at
startup, the app now skips wifi.Initialize / StartEventMonitoring and
guards every wifi.* wrapper against a nil backend. This prevents D-Bus
calls to fi.w1.wpa_supplicant1 from re-activating the daemon via
dbus-activation, honoring the "do nothing" intent of the Ethernet path.
The probed state is exposed in SystemStatus and rendered in the header
as a third pill ("Ethernet · <IP>"); a new "disabled" connectionState
covers the WiFi pill in this mode.
Probe the configured Ethernet interface (default eth0, overridable via
-ethernet-interface) at startup. If no DHCP-assigned IPv4 is present,
start the wpa_supplicant service so the WiFi backend has something to
talk to; otherwise leave it alone and rely on the wired uplink.
