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-media-replace/templates/generic-modal.twig.html

@@ -1,22 +0,0 @@
-<div class="remodal" data-remodal-id="{{remodalId}}" data-remodal-options="hashTracking: false">
-    <form method="post" onsubmit='return false;'>
-        {% for name, field in fields %}
-        {% if field.type %}
-        {% set value = data.value(name) %}
-        <div class="block block-{{field.type}}">
-            {% include ["forms/fields/#{field.type}/#{field.type}.html.twig", 'forms/fields/text/text.html.twig'] %}
-        </div>
-        {% endif %}
-        {% endfor %}
-
-        <div class="form-field grid">{{message}}</div>
-
-        <div class="button-bar">
-            <!--<div class="loading">-->
-            <!--{{ "Moving" }}... <i class="fa fa-spinner fa-spin"></i>-->
-            <!--</div>-->
-            <button class="button" style="visibility: visible" name="cancel">{{ "Cancel" }}</button>
-            <button class="button primary" style="visibility: visible" name="continue">{{ "Continue" }}</button>
-        </div>
-    </form>
-</div>