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/modular/form.html.twig

@@ -1,8 +0,0 @@
-<div class="modular-row form {{ page.header.class }}">
-  {{ content|raw }}
-  {% if config.plugins.form.modular_form_fix %}
-    {% include "forms/form.html.twig" with {form: forms({route: page.route})} %}
-  {% else %}
-    {% include "forms/form.html.twig" %}
-  {% endif %}
-</div>