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/admin/themes/grav/templates/partials/notification-themes-block.html.twig

@@ -1,6 +0,0 @@
-{% for entry_id, entry in notifications %}
-    <div class="alert {{ entry.type }} position-themes">
-        <a href="#" data-notification-action="hide-notification" data-notification-id="{{ entry.id }}" class="close hide-notification"><i class="fa fa-close"></i></a>
-        {{ entry.message|raw }}
-    </div>
-{% endfor %}