[rangaNP]

Summary

The tab-switcher checkmark followed the highlighted choice, making it hard to identify the page currently open. Keep the checkmark on the current tab while the highlight and border move between choices.

Changes

• Base the checkmark on the window's active tab, and announce “Current tab” through VoiceOver while preserving the selected candidate's accessibility state.

Testing

On macOS 27.2 with Xcode 27.2:

• swift test --no-parallel: all 918 package tests passed.
• Existing tab-switcher tests also passed separately (13 tests).
• Debug xcodebuild build-for-testing and Release xcodebuild build: succeeded.
• Native UI tests were compiled only; execution remains on CI.
• git diff --check: passed.

Screenshots or recording

The rebuilt Debug app was provided for local review; no screenshot attached. To check: move through the switcher choices and confirm the tick stays on the current tab, then switch and reopen to see the new current tab marked.

Checklist

• I reviewed the diff and kept the changes focused on this PR.
• I described the validation performed and any remaining limitations.
• I understand the changes and can explain them and address maintainer questions in review comments.