fix(control-pane): drop unused child_process spawn import (lint red on main)

Same openBrowser-extraction fallout as plan-canvas: control-pane.js kept
an import it no longer uses, failing eslint no-unused-vars on every CI
run. Verified: npx eslint scripts/control-pane.js clean.

scripts/control-pane.js

@@ -1,8 +1,6 @@
 #!/usr/bin/env node
 'use strict';
 
-const { spawn } = require('child_process');
-
 const {
   createControlPaneServer,
   parseArgs,