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/tab/tab.html.twig

@@ -1,8 +0,0 @@
-{% extends "forms/field.html.twig" %}
-
-{% block field %}
-  {% embed 'forms/default/fields.html.twig' with {name: field.name, fields: field.fields} %}
-    {% block outer_markup_field_open %}<div class="form-tab">{% endblock %}
-    {% block outer_markup_field_close %}</div>{% endblock %}
-  {% endembed %}
-{% endblock %}