CascaderEmpty stays hidden in inline mode

[focus0802]

Description

CascaderEmpty is rendered in the DOM but remains hidden when Cascader is used in inline mode.

Popup mode works because CascaderContent provides the named group/combobox-content ancestor and Base UI's data-empty state. Inline mode renders CascaderPanel without CascaderContent, so the group-data-empty/combobox-content:flex class on CascaderEmpty can never activate.

Reproduction

1. Render an inline Cascader with CascaderPanel, CascaderInput, CascaderList, and CascaderEmpty.
2. Enter a query that matches no items.
3. Inspect the DOM. The cascader-empty element exists with data-state="empty", but remains hidden.

Expected behavior

The empty message should be visible when an inline Cascader has no rendered items, matching popup Cascader and ComboboxEmpty behavior.

Suggested fix

Have inline CascaderPanel publish the same named-group and empty-state contract as CascaderContent: add group/combobox-content in inline mode and set data-empty when renderedItems.length === 0. This keeps CascaderEmpty aligned with ComboboxEmpty without a forced visibility override or conditional unmount.

Screenshots

Before

After