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/messages.html.twig

@@ -1,14 +0,0 @@
-{% set admin_messages = admin.messages|merge(admin.getTempMessages()) %}
-{% set form_message = form.message %}
-<div id="messages" class="top-notifications-container{{ admin_messages|length or form_message ? ' default-box-shadow' : '' }}">
-    <div class="single-notification info alert hidden" data-gpm-grav></div>
-    {%- for message in admin_messages -%}
-    <div class="{{ message.scope }} alert">{{ message.message|raw }}</div>
-    {%- endfor -%}
-    {%- if form_message -%}
-    <div class="error alert">{{ form_message|raw }}</div>
-    {%- endif -%}
-    {%- for message in plugin_messages -%}
-        <div class="{{ message.scope }} alert">{{ message.message|raw }}</div>
-    {%- endfor -%}
-</div>