Add the Fyne desktop app (M5)

A cross-platform desktop UI over the same client service: status,
routes with add/remove/copy/open, live logs, settings, official-profile
import, and start/stop. It uses the existing JSON config and offers to
stop a running CLI daemon so the two do not fight over routes. The app
can autostart the service, refreshes status/config every few seconds,
and builds as a macOS .app via scripts/build-desktop-app.sh.

cmd/tunnel-desktop/main.go

@@ -1,11 +1,15 @@
 package main
 
 import (
+	"flag"
+
 	"gitea.tzgyn.dev/TZGyn/tunnel/internal/desktop"
 )
 
 var version = "dev"
 
 func main() {
-	desktop.Run(version)
+	autostart := flag.Bool("autostart", false, "start the tunnel service when the app launches")
+	flag.Parse()
+	desktop.Run(version, *autostart)
 }