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/event-dispatcher/LegacyEventDispatcherProxy.php

@@ -1,31 +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\Component\EventDispatcher;
-
-use Symfony\Contracts\EventDispatcher\EventDispatcherInterface;
-
-trigger_deprecation('symfony/event-dispatcher', '5.1', '%s is deprecated, use the event dispatcher without the proxy.', LegacyEventDispatcherProxy::class);
-
-/**
- * A helper class to provide BC/FC with the legacy signature of EventDispatcherInterface::dispatch().
- *
- * @author Nicolas Grekas <p@tchwork.com>
- *
- * @deprecated since Symfony 5.1
- */
-final class LegacyEventDispatcherProxy
-{
-    public static function decorate(?EventDispatcherInterface $dispatcher): ?EventDispatcherInterface
-    {
-        return $dispatcher;
-    }
-}