Tests table: path tooltips and row links are not keyboard-accessible

[alanpeixinho]

On the tests table, keyboard users cannot reliably reach or see focus for some interactive elements:

1. Path tooltips — Path cells use non-focusable div elements as tooltip triggers. Collapsed group paths and leaf paths are skipped when tabbing, so tooltips are only usable with a mouse.
2. Row links — Table cells use overflow-hidden, which clips the default focus ring on full-cell links. Focus is hard to see when navigating with Tab.