docs: popover occlusion verified after the coverage-scan memo

Follow-up to 2f8b6d8. With the page dropdown open over the 1359-row package
list: hovering inside the popover highlights the menu item and leaves every row
beneath unhighlighted; hovering the same height outside it highlights the row
and clears the menu item, with the row's highlight band stopping exactly at the
popover's left edge. Both directions including hover-out, so the memo preserves
the occlusion behaviour it guards.

Co-Authored-By: Claude Opus 5 <[email protected]>