fix(debugger): extract MarteController into an importable controller package

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.

Client/debugger/main.go

@@ -10,6 +10,8 @@ import (
 	"net/http"
 	"os"
 
+	"marte2debugger/controller"
+
 	"marte2/common/wshub"
 )
 
@@ -21,7 +23,7 @@ var staticFiles embed.FS
 func main() {
 	addr := flag.String("addr", ":7777", "HTTP listen address")
 	sourcesFile := flag.String("sources-file", "", "JSON file for persistent source list")
-	flag.BoolVar(&dangerousCommandsEnabled, "enable-dangerous-commands", false,
+	flag.BoolVar(&controller.DangerousCommandsEnabled, "enable-dangerous-commands", false,
 		"Allow FORCE/PAUSE/RESUME/STEP/BREAK/MSG commands from the browser (CR-4 safety gate)")
 	flag.Parse()
 
@@ -29,7 +31,7 @@ func main() {
 	sm := wshub.NewSourceManager(hub, *sourcesFile)
 	hub.SetSourceManager(sm)
 
-	ctrl := NewMarteController(hub)
+	ctrl := controller.NewMarteController(hub)
 
 	go hub.Run()