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/elements/elements.html.twig

@@ -1,20 +0,0 @@
-{% extends "forms/fields/select/select.html.twig" %}
-{% set field = field|merge({ autocomplete: 'off' }) %}
-
-{% if grav.admin is not defined %}
-{# load some frontend CSS/JS #}
-{% endif %}
-
-{% block global_attributes %}
-  data-grav-elements="{{ field.name }}"
-  {{ parent() }}
-{% endblock %}
-
-{% block field %}
-  {{ parent() }}
-  {% set parent_name = field.name %}
-  {% set parent_value = value %}
-  {% if fields|length %}
-    {% include 'forms/default/fields.html.twig' with {name: parent_name, fields: field.fields} %}
-  {% endif %}
-{% endblock %}