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/form/templates/forms/fields/spacer/spacer.html.twig

@@ -1,19 +0,0 @@
-{% extends "forms/field.html.twig" %}
-
-{% block field %}
-<div class="form-field form-spacer {{ field.classes }}">
-    {% if field.title %}
-        <{{ field.title_type|default('h3') }}>{{- field.title|t|raw -}}</{{ field.title_type|default('h3') }}>
-    {% endif %}
-
-    {% if field.markdown %}
-        {{- field.text|t|markdown|raw -}}
-    {% else %}
-        <p>{{- field.text|t|raw -}}</p>
-    {% endif %}
-
-    {% if field.underline %}
-    <hr />
-    {% endif %}
-</div>
-{% endblock %}