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/service-contracts/Test/ServiceLocatorTest.php

@@ -1,23 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Contracts\Service\Test;
-
-class_alias(ServiceLocatorTestCase::class, ServiceLocatorTest::class);
-
-if (false) {
-    /**
-     * @deprecated since PHPUnit 9.6
-     */
-    class ServiceLocatorTest
-    {
-    }
-}