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/frontmatter/frontmatter.html.twig

@@ -1,10 +0,0 @@
-{# Deprecated field. Alias to editor/editor.html.twig #}
-
-{% extends "forms/fields/editor/editor.html.twig" %}
-{% set codemirrorOptions = {'mode': 'yaml', 'indentUnit': 4, ignore: ['code'], 'autofocus': true, 'indentWithTabs': false, 'lineNumbers': true, 'gutters': ["CodeMirror-lint-markers"]}|merge(field.codemirror|default({})) %}
-
-{# backward compatibility #}
-{% if field.showPreview %}
-    {% set codemirrorOptions = codemirrorOptions|merge({'ignore': []}) %}
-{% endif %}
-{# end backward compatibility #}