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/elements.js

@@ -1,12 +0,0 @@
-import $ from 'jquery';
-
-$(document).on('change', '[data-grav-elements] select', (event) => {
-  const target = $(event.currentTarget);
-  const value = target.val();
-  const id = target.closest('[data-grav-elements]').data('gravElements');
-
-  $(`[id^="${id}_"]`).css('display', 'none');
-  $(`[id="${id}__${value}"]`).css('display', 'inherit');
-});
-
-$('[data-grav-elements] select').trigger('change');