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/fieldset/fieldset.html.twig

@@ -1,12 +0,0 @@
-{% extends "forms/field.html.twig" %}
-{% set scope = field.nest_id ? scope ~ field.name ~ '.' : scope %}
-
-{% block field %}
-<fieldset {% if field.id is defined %}id="{{ field.id }}"{% endif %} {% if field.classes is defined %}class="{{ field.classes }}" {% endif %}>
-  {% if field.legend %}
-    <legend>{{ field.legend|t }}</legend>
-  {% endif %}
-
-  {% include 'forms/default/fields.html.twig' with {name: field.name, fields: field.fields} %}
-</fieldset>
-{% endblock %}