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/app/forms/fields/folder.js

@@ -1,20 +0,0 @@
-import $ from 'jquery';
-
-const Regenerate = (field = '[name="data[folder]"]') => {
-    const element = $(field);
-    const title = $('[name="data[header][title]"]');
-    const slug = $.slugify(title.val(), {custom: {"'": ''}});
-
-    element.addClass('highlight').val(slug);
-
-    setTimeout(() => element.removeClass('highlight'), 500);
-};
-
-$(document).on('click', '[data-regenerate]', (event) => {
-    const target = $(event.currentTarget);
-    const field = $(target.data('regenerate'));
-
-    Regenerate(field);
-});
-
-export default Regenerate;