Move plugins to manifest, pin Docker version, add Makefile

- Add plugins.txt listing all plugins for reproducible installs
- Add Makefile with setup/start/stop/install-plugins targets
- Remove user/plugins/ from git tracking
- Pin Docker image to 1.7.49.5-ls244

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/email/vendor/symfony/polyfill-intl-idn/Info.php

@@ -1,23 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com> and Trevor Rowbotham <trevor.rowbotham@pm.me>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Polyfill\Intl\Idn;
-
-/**
- * @internal
- */
-class Info
-{
-    public $bidiDomain = false;
-    public $errors = 0;
-    public $validBidiDomain = true;
-    public $transitionalDifferent = false;
-}