fix: set DBTabItem selected state correctly

[milan-w]

Set (aria-)selected state via listener on parent tablist to also react on de-selection of item. Closes #5288

Proposed changes

Each tab item holds an internal state _selected to keep track of the active tab. However before this change the state function did not correctly react to a de-selection because the event was only triggered on the newly active tab.
Now each item registers an event listener on the parent component and sets de/selected according to this event.

The playwright test for the tab components has also been refactored slightly to eliminate an unneccesary file write process.

Types of changes

• Bugfix (non-breaking change that fixes an issue)

• New feature (non-breaking change which adds functionality)

• Refactoring (improvements to existing components or architectural decisions)

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

• Documentation Update (if none of the other choices apply)

• I have added tests that prove my fix is effective or that my feature works

• I have added necessary documentation (if appropriate)

🔭🐙🐈 Test this branch here: https://design-system.deutschebahn.com/core-web/review/fix-tab-item-selected-state

[changeset-bot]

🦋 Changeset detected

Latest commit: 85ac495

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 9 packages

Name	Type
@db-ux/core-components	Patch
@db-ux/ngx-core-components	Patch
@db-ux/react-core-components	Patch
@db-ux/wc-core-components	Patch
@db-ux/v-core-components	Patch
@db-ux/core-foundations	Patch
@db-ux/core-stylelint	Patch
@db-ux/core-migration	Patch
@db-ux/agent-cli	Patch

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[Copilot]

Pull Request Overview

This PR fixes the internal state management of the DBTabItem component to correctly track and update the _selected state, which improves accessibility by ensuring aria-selected attributes are properly set for screen readers. The key changes include:

• Replaced file-based test state management with an in-memory variable for testing the onIndexChange callback
• Fixed tab index calculation in DBTabs by using children instead of childNodes to exclude text nodes
• Added event listener logic to synchronize _selected state across tabs when selection changes

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
packages/components/src/components/tabs/tabs.spec.tsx	Replaced file system operations with module-scoped variable for testing tab index changes
packages/components/src/components/tabs/tabs.lite.tsx	Fixed index calculation by using list.children instead of list.childNodes and renamed variable from indices to tabIndex
packages/components/src/components/tab-item/tab-item.lite.tsx	Added setSelectedOnChange function, event listener management, and improved _selected state tracking to fix aria-selected behavior
.changeset/sharp-pumas-obey.md	Added changeset documenting the bug fix for DBTabItem internal state and accessibility improvements

Comments suppressed due to low confidence (1)

packages/components/src/components/tabs/tabs.spec.tsx:27

• The comp component is defined at module scope with a closure over the module-scoped tabIndex variable. Since this component is reused across multiple tests (lines 31, 36, 48, 65, 70), all tests will mutate the same shared tabIndex variable. This creates test interdependencies and can lead to flaky tests depending on execution order.

Consider creating the component inside each test that needs it, or using a factory function that returns a fresh component instance with its own state.

const comp: any = (
	<DBTabs onIndexChange={(index: number) => (tabIndex = index)}>
		<DBTabList>
			<DBTabItem data-testid="test">Test 1</DBTabItem>
			<DBTabItem data-testid="test2">Test 2</DBTabItem>
			<DBTabItem>Test 3</DBTabItem>
		</DBTabList>

		<DBTabPanel>TestPanel 1</DBTabPanel>

		<DBTabPanel>TestPanel 2</DBTabPanel>

		<DBTabPanel>TestPanel 3</DBTabPanel>
	</DBTabs>
);