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/langswitcher/templates/partials/langswitcher.html.twig

@@ -1,15 +0,0 @@
-{% extends 'partials/langswitcher-logic.html.twig' %}
-
-{% block language_block_start %}
-<ul class="langswitcher">
-{% endblock %}
-
-{% block language_block_end %}
-</ul>
-{% endblock %}
-
-{% block language_item %}
-    {% if show_language %}
-    <li><a href="{{ lang_url ~ uri.params ~ (uri.query|length > 1 ? '?' ~ uri.query) }}" class="external {{ active_class }}">{% include 'partials/langswitcher-' ~ display_format ~ '.html.twig' %}</a></li>
-    {% endif %}
-{% endblock %}