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/layouts/form.html.twig

@@ -1,4 +0,0 @@
-{# DEPRECATED: Do not override this file! Use forms/layouts/form/[FORM_LAYOUT]-form.html.twig instead #}
-
-{% set layout = layout ?? form.layout ?? 'default' %}
-{% extends ["forms/layouts/form/#{layout}-form.html.twig", 'forms/layouts/form/default-form.html.twig'] %}