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/Handler/BatchHandlerInterface.php

@@ -1,34 +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\Handler;
-
-/**
- * @author Nicolas Grekas <p@tchwork.com>
- */
-interface BatchHandlerInterface
-{
-    /**
-     * @param Acknowledger|null $ack The function to call to ack/nack the $message.
-     *                               The message should be handled synchronously when null.
-     *
-     * @return mixed The number of pending messages in the batch if $ack is not null,
-     *               the result from handling the message otherwise
-     */
-    // public function __invoke(object $message, ?Acknowledger $ack = null): mixed;
-
-    /**
-     * Flushes any pending buffers.
-     *
-     * @param bool $force Whether flushing is required; it can be skipped if not
-     */
-    public function flush(bool $force): void;
-}