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/messenger/Middleware/ValidationMiddleware.php

@@ -1,50 +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\Messenger\Middleware;
-
-use Symfony\Component\Messenger\Envelope;
-use Symfony\Component\Messenger\Exception\ValidationFailedException;
-use Symfony\Component\Messenger\Stamp\ValidationStamp;
-use Symfony\Component\Validator\Validator\ValidatorInterface;
-
-/**
- * @author Tobias Nyholm <tobias.nyholm@gmail.com>
- */
-class ValidationMiddleware implements MiddlewareInterface
-{
-    private $validator;
-
-    public function __construct(ValidatorInterface $validator)
-    {
-        $this->validator = $validator;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function handle(Envelope $envelope, StackInterface $stack): Envelope
-    {
-        $message = $envelope->getMessage();
-        $groups = null;
-        /** @var ValidationStamp|null $validationStamp */
-        if ($validationStamp = $envelope->last(ValidationStamp::class)) {
-            $groups = $validationStamp->getGroups();
-        }
-
-        $violations = $this->validator->validate($message, null, $groups);
-        if (\count($violations)) {
-            throw new ValidationFailedException($message, $violations);
-        }
-
-        return $stack->next()->handle($envelope, $stack);
-    }
-}