Create the kid account in the input group

Sunshine (running in the kid's session) needs /dev/uinput — group
'input' — to create the virtual mouse/keyboard for Moonlight remote
control; without it the input stream hangs at "establishment" while
video works. Found on hardware; on-box fix is usermod -aG input.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

iso-config.toml

@@ -13,3 +13,5 @@ groups = ["wheel"]
 [[customizations.user]]
 name = "kid"
 password = "bc250console"
+# input: Sunshine needs /dev/uinput access for Moonlight remote control
+groups = ["input"]