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/automagic-images/vendor/php-http/promise/composer.json

@@ -1,38 +0,0 @@
-{
-    "name": "php-http/promise",
-    "description": "Promise used for asynchronous HTTP requests",
-    "license": "MIT",
-    "keywords": ["promise"],
-    "homepage": "http://httplug.io",
-    "authors": [
-        {
-            "name": "Joel Wurtz",
-            "email": "joel.wurtz@gmail.com"
-        },
-        {
-            "name": "Márk Sági-Kazár",
-            "email": "mark.sagikazar@gmail.com"
-        }
-    ],
-    "require": {
-        "php" : "^7.1 || ^8.0"
-    },
-    "require-dev": {
-        "friends-of-phpspec/phpspec-code-coverage" : "^4.3.2",
-        "phpspec/phpspec": "^5.1.2 || ^6.2"
-    },
-    "autoload": {
-        "psr-4": {
-            "Http\\Promise\\": "src/"
-        }
-    },
-    "scripts": {
-        "test": "vendor/bin/phpspec run",
-        "test-ci": "vendor/bin/phpspec run -c phpspec.yml.ci"
-    },
-    "extra": {
-        "branch-alias": {
-            "dev-master": "1.1-dev"
-        }
-    }
-}