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/cli/ClearQueueFailuresCommand.php

@@ -1,39 +0,0 @@
-<?php
-namespace Grav\Plugin\Console;
-
-use Grav\Common\Grav;
-use Grav\Console\ConsoleCommand;
-use Grav\Plugin\Email\Email;
-use Symfony\Component\Console\Input\InputOption;
-
-/**
- * Class FlushQueueCommand
- * @package Grav\Console\Cli\
- * @deprecated 4.0 Switched from Swiftmailer to Symfony/Mailer - No longer supported
- */
-class ClearQueueFailuresCommand extends ConsoleCommand
-{
-    /** @var array */
-    protected $options = [];
-
-    /**
-     * @return void
-     */
-    protected function configure()
-    {
-        $this
-            ->setName('clear-queue-failures')
-            ->setAliases(['clearqueue'])
-            ->setDescription('DEPRECATED: Clears any queue failures that have accumulated')
-            ->setHelp('The <info>clear-queue-failures</info> command clears any queue failures that have accumulated');
-    }
-
-    /**
-     * @return int
-     * @deprecated 4.0 Switched from Swiftmailer to Symfony/Mailer - No longer supported
-     */
-    protected function serve()
-    {
-        return 0;
-    }
-}