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/draft-preview/vendor/composer/installed.php

@@ -1,24 +0,0 @@
-<?php return array (
-  'root' => 
-  array (
-    'pretty_version' => 'dev-main',
-    'version' => 'dev-main',
-    'aliases' => 
-    array (
-    ),
-    'reference' => '13f73587e8398e820c46291a56c36985f46afc1b',
-    'name' => 'bitstarr/draft-preview',
-  ),
-  'versions' => 
-  array (
-    'bitstarr/draft-preview' => 
-    array (
-      'pretty_version' => 'dev-main',
-      'version' => 'dev-main',
-      'aliases' => 
-      array (
-      ),
-      'reference' => '13f73587e8398e820c46291a56c36985f46afc1b',
-    ),
-  ),
-);