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/formdata.html.twig

@@ -1,20 +0,0 @@
-{% extends 'partials/base.html.twig' %}
-
-{% if form is null %}
-    {% set form = grav.session.getFlashObject('form') %}
-{% endif  %}
-
-{% block content %}
-    {{ content|raw }}
-
-    {% if form %}
-        {% include 'partials/form-messages.html.twig' %}
-
-        <p>{{ 'PLUGIN_FORM.DATA_SUMMARY'|t }}</p>
-
-        {% include "forms/data.html.twig" %}
-    {% else %}
-        <div class="notices warning yellow"><p>{{ 'PLUGIN_FORM.NO_FORM_DATA'|t }}</p></div>
-    {% endif %}
-
-{% endblock %}