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/composer/autoload_files.php

@@ -1,13 +0,0 @@
-<?php
-
-// autoload_files.php @generated by Composer
-
-$vendorDir = dirname(__DIR__);
-$baseDir = dirname($vendorDir);
-
-return array(
-    '6e3fae29631ef280660b3cdad06f25a8' => $vendorDir . '/symfony/deprecation-contracts/function.php',
-    'a4a119a56e50fbb293281d9a48007e0e' => $vendorDir . '/symfony/polyfill-php80/bootstrap.php',
-    'e69f7f6ee287b969198c3c9d6777bd38' => $vendorDir . '/symfony/polyfill-intl-normalizer/bootstrap.php',
-    'f598d06aa772fa33d905e87be6398fb1' => $vendorDir . '/symfony/polyfill-intl-idn/bootstrap.php',
-);