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/forms/fields/mediapicker/mediapicker.html.twig

@@ -1,17 +0,0 @@
-{% extends "forms/fields/text/text.html.twig" %}
-
-{% set unique_identifier = random_string() %}
-
-{% block global_attributes %}
-{{ parent() }}
-data-mediapicker-modal-trigger
-data-grav-mediapicker-unique-identifier="{{ unique_identifier }}"
-{% endblock %}
-
-
-{% block contents %}
-{{ parent() }}
-<div class="remodal remodal-mediapicker" data-remodal-mediapicker data-remodal-unique-identifier="{{ unique_identifier }}" data-remodal-options="hashTracking: false">
-    {% include 'partials/media-list-wrapper.html.twig' with { is_modal: true } %}
-</div>
-{% endblock %}