fix(frontend): restore antd5 Tag trailing margin for layout parity

antd 6 removed the Tag's default margin-inline-end: 8px in favor of
parents spacing tags via flex/Space gaps. App layouts predate that and
rely on the v5 default — most visibly the dashboard header, where the
Published tag sat flush against the metadata bar. Restore the margin in
GlobalStyles (to be removed once Tag-adjacent layouts declare their own
gaps) and pin it with a computed-style regression test that exercises
the provider -> GlobalStyles -> Tag chain.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: rusackas

superset-frontend/packages/superset-core/src/theme/GlobalStyles.tsx

@@ -105,6 +105,16 @@ export const GlobalStyles = () => {
           cursor: pointer;
         }
 
+        // antd 6 removed the Tag's default trailing margin (v5 shipped
+        // margin-inline-end: 8px on every tag) in favor of parents spacing
+        // tags via flex/Space gaps. The app's layouts predate that and rely
+        // on the v5 default (e.g. the dashboard header's Published tag),
+        // so restore it for visual parity. Remove once Tag-adjacent layouts
+        // declare their own gaps.
+        .ant-tag {
+          margin-inline-end: ${theme.marginXS}px;
+        }
+
         // Override geostyler CSS that hides AntD ColorPicker alpha input
         // See: https://github.com/apache/superset/issues/34721
         .ant-color-picker .ant-color-picker-alpha-input {

superset-frontend/packages/superset-ui-core/src/components/antdDomContract.test.tsx

@@ -33,7 +33,7 @@
  */
 import { render } from '@superset-ui/core/spec';
 // eslint-disable-next-line no-restricted-imports
-import { Collapse, Modal, Popover, Steps, Tabs, Tooltip } from 'antd';
+import { Collapse, Modal, Popover, Steps, Tabs, Tag, Tooltip } from 'antd';
 import { Select } from './Select';
 
 const antClasses = (root: ParentNode): string[] => {
@@ -224,3 +224,17 @@ test('Modal body class (many *.styles.ts modal overrides target it)', () => {
   );
   expect(antClasses(document.body)).toContain('ant-modal-body');
 });
+
+test('Tag keeps its v5 trailing margin (GlobalStyles parity rule)', () => {
+  // antd 6 removed the Tag's default margin-inline-end: 8px, expecting
+  // parents to space tags via flex/Space gaps. App layouts rely on the v5
+  // default (e.g. the dashboard header's Published tag sat flush against
+  // the metadata bar without it), so GlobalStyles restores it. The spec
+  // renderer mounts SupersetThemeProvider, which renders GlobalStyles, so
+  // the computed style asserts the whole chain.
+  const { getByText } = render(<Tag>spacing</Tag>);
+  const tag = getByText('spacing').closest('.ant-tag') as HTMLElement;
+  expect(getComputedStyle(tag).getPropertyValue('margin-inline-end')).toBe(
+    '8px',
+  );
+});