Client/debugger was entirely package main, which Go forbids importing from
another module ("is a program, not an importable package") -- discovered
while wiring the new debugclient E2E tool against NewHeadlessMarteController.
Move martecontrol.go and its test into a new marte2debugger/controller
subpackage (package controller) and update Client/debugger/main.go to call
controller.NewMarteController/controller.DangerousCommandsEnabled. No
behavioral change to the browser-facing server.
Martino Ferrari