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/form/templates/forms/fields/avatar/avatar.html.twig

@@ -1,10 +0,0 @@
-{% extends "forms/field.html.twig" %}
-
-{% block field %}
-{% set avatar = form.value('avatar') %}
-{% if avatar %}
-    <label class="{{ field.classes }}"><img class="{{ field.img_classes }}" style="max-width:200px;" src="{{ base_url_simple ~ '/' ~ (avatar|first).path }}" /></label>
-{% else %}
-    <label class="{{ field.classes }}"><img class="{{ field.img_classes }}" src="https://www.gravatar.com/avatar/{{ form.value('email')|md5 }}?s=200" /></label>
-{% endif %}
-{% endblock %}