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/admin/themes/grav/templates/partials/javascripts.html.twig

@@ -1,11 +0,0 @@
-{% do assets.add('jquery',101) %}
-{% if authorize(['admin.login', 'admin.super']) %}
-{% do assets.addJs(theme_url~'/js/vendor.min.js', { 'loading':'defer' }) %}
-{% do assets.addJs(theme_url~'/js/admin.min.js' , { 'loading':'defer' }) %}
-
-{% if browser.getBrowser == 'msie' or browser.getBrowser == 'edge' %}
-    {% do assets.addJs(theme_url~'/js/form-attr.polyfill.js') %}
-{% endif %}
-
-{% include 'partials/javascripts-extra.html.twig' ignore missing %}
-{% endif %}