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/mailer/composer.json

@@ -1,43 +0,0 @@
-{
-    "name": "symfony/mailer",
-    "type": "library",
-    "description": "Helps sending emails",
-    "keywords": [],
-    "homepage": "https://symfony.com",
-    "license": "MIT",
-    "authors": [
-        {
-            "name": "Fabien Potencier",
-            "email": "fabien@symfony.com"
-        },
-        {
-            "name": "Symfony Community",
-            "homepage": "https://symfony.com/contributors"
-        }
-    ],
-    "require": {
-        "php": ">=7.2.5",
-        "egulias/email-validator": "^2.1.10|^3|^4",
-        "psr/event-dispatcher": "^1",
-        "psr/log": "^1|^2|^3",
-        "symfony/deprecation-contracts": "^2.1|^3",
-        "symfony/event-dispatcher": "^4.4|^5.0|^6.0",
-        "symfony/mime": "^5.2.6|^6.0",
-        "symfony/polyfill-php80": "^1.16",
-        "symfony/service-contracts": "^1.1|^2|^3"
-    },
-    "require-dev": {
-        "symfony/http-client": "^4.4|^5.0|^6.0",
-        "symfony/messenger": "^4.4|^5.0|^6.0"
-    },
-    "conflict": {
-        "symfony/http-kernel": "<4.4"
-    },
-    "autoload": {
-        "psr-4": { "Symfony\\Component\\Mailer\\": "" },
-        "exclude-from-classmap": [
-            "/Tests/"
-        ]
-    },
-    "minimum-stability": "dev"
-}