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/service-contracts/composer.json

@@ -1,42 +0,0 @@
-{
-    "name": "symfony/service-contracts",
-    "type": "library",
-    "description": "Generic abstractions related to writing services",
-    "keywords": ["abstractions", "contracts", "decoupling", "interfaces", "interoperability", "standards"],
-    "homepage": "https://symfony.com",
-    "license": "MIT",
-    "authors": [
-        {
-            "name": "Nicolas Grekas",
-            "email": "p@tchwork.com"
-        },
-        {
-            "name": "Symfony Community",
-            "homepage": "https://symfony.com/contributors"
-        }
-    ],
-    "require": {
-        "php": ">=7.2.5",
-        "psr/container": "^1.1",
-        "symfony/deprecation-contracts": "^2.1|^3"
-    },
-    "conflict": {
-        "ext-psr": "<1.1|>=2"
-    },
-    "suggest": {
-        "symfony/service-implementation": ""
-    },
-    "autoload": {
-        "psr-4": { "Symfony\\Contracts\\Service\\": "" }
-    },
-    "minimum-stability": "dev",
-    "extra": {
-        "branch-alias": {
-            "dev-main": "2.5-dev"
-        },
-        "thanks": {
-            "name": "symfony/contracts",
-            "url": "https://github.com/symfony/contracts"
-        }
-    }
-}