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/deprecation-contracts/function.php

@@ -1,27 +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.
- */
-
-if (!function_exists('trigger_deprecation')) {
-    /**
-     * Triggers a silenced deprecation notice.
-     *
-     * @param string $package The name of the Composer package that is triggering the deprecation
-     * @param string $version The version of the package that introduced the deprecation
-     * @param string $message The message of the deprecation
-     * @param mixed  ...$args Values to insert in the message using printf() formatting
-     *
-     * @author Nicolas Grekas <p@tchwork.com>
-     */
-    function trigger_deprecation(string $package, string $version, string $message, ...$args): void
-    {
-        @trigger_error(($package || $version ? "Since $package $version: " : '').($args ? vsprintf($message, $args) : $message), \E_USER_DEPRECATED);
-    }
-}