Popup tabs now follow the WAI-ARIA tabs keyboard pattern: Left and Right
wrap from the last tab to the first and back, and Home and End jump to the
ends of the strip. The strip collects its focusable tabs from the focus
chain in one handler shared by the overview, global, and provider tabs,
and TabStripGeometry.js picks the target index.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>