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/backups-button.html.twig

@@ -1,21 +0,0 @@
-<div class="button-group">
-    {% set profiles = grav.backups.getBackupProfiles() %}
-    {% set backup_url = uri.addNonce(base_url_relative ~ "/backup.json/id" ~ config.system.param_sep ~ "%BACKUP_ID/task" ~ config.system.param_sep ~ "backup", 'admin-form', 'admin-nonce') %}
-
-    <button class="button" data-backup data-ajax="{{ backup_url|replace({'%BACKUP_ID':'0'}) }}">
-        <i class="fa fa-life-ring"></i> {{ "PLUGIN_ADMIN.BACKUP_NOW"|t }}
-    </button>
-    <button type="button" class="button dropdown-toggle" data-toggle="dropdown">
-        <i class="fa fa-caret-down"></i>
-    </button>
-    <ul class="dropdown-menu">
-        {% for id, profile in profiles %}
-            <li>
-                <a data-backup data-ajax="{{ backup_url|replace({'%BACKUP_ID':id}) }}" class="button">{{ profile.name }}</a>
-            </li>
-        {% endfor %}
-        <li>
-            <a href="{{ admin_route('/tools/backups') }}" class="button">Backups Manager</a>
-        </li>
-    </ul>
-</div>