Default Admin: Link field help text is squeezed beside the URL field

Problem/Motivation

In the Default Admin theme, the help text for a Link field URL is forced beside the URL input when the widget is rendered inside a multi-value table. The long instructions then wrap into a narrow column and make the form difficult to read. This is a Default Admin theme issue; the earlier report was filed under Claro and is closed as outdated.

Steps to reproduce

1. Use Default Admin as the administration theme.
2. Create or edit an entity type with a multi-value Link field that has URL help text.
3. Open the entity add/edit form and inspect a Link field row.

On this site, the issue is visible in the Significant links field on the Place form at /node/add/place.

Expected: The URL label and input remain together, and the help text appears below the URL input with clear spacing above it.

Actual: Default Admin applies a flex layout to td > .form-item. The URL field help text is laid out next to the input and gets squeezed into the remaining table width.

Proposed resolution

Adjust Default Admin table CSS for Link field form items with descriptions. Keep the label and URL control on one line on desktop, place the description below the control with top spacing, and stack the label, input, and description on narrow screens.

Remaining tasks

Review and test the attached patch. The patch was applied cleanly to Drupal 11.4.7, followed by a cache rebuild; I checked the rendered form at 1600px and 390px widths.

User interface changes

CSS-only change to the placement and wrapping of URL help text in Default Admin multi-value Link widgets.