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/pages/page/unset.js

@@ -1,18 +0,0 @@
-import $ from 'jquery';
-
-$(document).on('click', '.dz-unset', function() {
-
-    const file_upload = $(this).closest('.files-upload');
-    $(this).closest('.dz-image-preview').remove();
-    const unset_image = $(this).closest('.dz-image-preview').find('[data-dz-name]').text().trim();
-    const images = JSON.parse(file_upload.find('input[data-grav-field="hidden"]').val()) || {};
-    let image_array = {};
-
-    $.each(images, function(ind, obj) {
-        if (!ind.endsWith(unset_image)) {
-            image_array[ind] = obj;
-        }
-    });
-
-    file_upload.find('input[data-grav-field="hidden"]').val(JSON.stringify(image_array));
-});