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/login-logo.html.twig

@@ -1,14 +0,0 @@
-{% if config.plugins.admin.logo_text %}
-    <h1 class="text-logo">
-        {{ config.plugins.admin.logo_text }}
-    </h1>
-{% else %}
-    <h1 class="{{ custom_login_logo ? 'custom-logo' : 'default-logo' }}">
-        {{ title }}
-        {% if custom_login_logo %}
-            <img src="{{ url(custom_login_logo) }}" title="Login" />
-        {% else %}
-            {% include('@admin-images/logo.svg') %}
-        {% endif %}
-    </h1>
-{% endif %}