Fix responsive image-region preview spacing

src/web/public/css/theme-custom.css

@@ -3330,6 +3330,12 @@ html[data-bs-theme='dark'] .template-field-card .tox .tox-collection {
 
 .slide-image-region-preview-tools > .slide-image-region-preview-box {
   min-width: 0;
+  justify-items: stretch;
+}
+
+.slide-image-region-preview-tools .slide-image-region-preview-shell,
+.slide-image-region-preview-tools .slide-image-region-preview {
+  max-width: none;
 }
 
 .slide-image-region-crop {

test/media-library.test.js

@@ -294,6 +294,15 @@ test('regenerated crop pixels preserve cropper rotation and flips', async () =>
   }
 });
 
+test('image crop preview fills its responsive column without right-aligned thumbnail padding', () => {
+  const stylesheet = fs.readFileSync(path.join(__dirname, '../src/web/public/css/theme-custom.css'), 'utf8');
+  const box = stylesheet.match(/^\.slide-image-region-preview-tools > \.slide-image-region-preview-box\s*\{([^}]+)\}/m);
+  assert.ok(box);
+  assert.match(box[1], /min-width:\s*0;/);
+  assert.match(box[1], /justify-items:\s*stretch;/);
+  assert.match(stylesheet, /\.slide-image-region-preview-tools \.slide-image-region-preview-shell,\s*\.slide-image-region-preview-tools \.slide-image-region-preview\s*\{\s*max-width:\s*none;/);
+});
+
 test('editor offers the cropper and player uses the crop copy while retaining original metadata', () => {
   const modules = {};
   const browserWindow = {