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.
Add a sink func(v any) field so MarteController's event stream can be
routed somewhere other than the browser WebSocket hub. NewMarteController
now sets sink to broadcast through the hub as before; a new
NewHeadlessMarteController(sink) constructor builds an instance with
hub == nil for the upcoming debugclient E2E tool. Direct m.hub.* calls
(SetSourceState/UpdateConfigForSource/PushDataForSource) are now guarded
with nil checks so a headless controller doesn't panic.
Martino Ferrari