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/forms/fields/columns/columns.html.twig

@@ -1,8 +0,0 @@
-{% extends "forms/field.html.twig" %}
-
-{% block field %}
-<div class="form-columns grid pure-g">
-    {% set cols = field.fields|length %}
-    {% include 'forms/default/fields.html.twig' with {name: field.name|parent_field, fields: field.fields, fallback_field: 'column', cols: cols} %}
-</div>
-{% endblock %}