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-twofa.html.twig

@@ -1,20 +0,0 @@
-{% embed 'partials/login.html.twig' with {title:'Grav 2-Factor Authentication', redirect: admin.session.redirect} %}
-
-{% block integration %}
-{% endblock %}
-
-{% block form %}
-    {% embed 'forms/default/fields.html.twig' with {name: null, fields: form.fields} %}
-        {% block inner_markup_field_open %}<div>{% endblock %}
-        {% block inner_markup_field_close %}</div>{% endblock %}
-    {% endembed %}
-
-    <div class="{{ form_button_outer_classes ?: 'form-actions primary-accent' }}">
-        <div class="form-actions primary-accent">
-            <button type="submit" class="button primary" name="task" value="twofa"><i class="fa fa-sign-in"></i> {{ 'PLUGIN_LOGIN.BTN_LOGIN'|t }}</button>
-        </div>
-    </div>
-
-{% endblock %}
-
-{% endembed %}