The narrow-viewport overlay for a collapsed zone is `absolute inset-y-0` —
it starts at the viewport's top edge with its tab strip (SESSIONS | BOTS) as
the first child, so on macOS the strip slides under the traffic lights.
Docked zones already reserve that band (TreeGroup: useWindowControlsOverlap
-> paddingTop plus an absolute [-webkit-app-region:drag] spacer; top-edge
zones use usePanelTitlebar), but the overlay used neither.
Reserve it the same way: measure the native controls rect against the
overlay element and pad the strip below it, keeping the band a window-drag
target via the drag-region spacer. The overlay's data attribute now carries
the revealed pane id (it was a constant empty string), which the regression
test uses as its selector.
Salvaged from PR #110034 by Muhammed Emin Boydak (the overlap hookup, the
paddingTop + drag spacer, and the 34px-reservation test), adapted to the
current file (NO_PANE_GROUP import, per-pane data attribute).
Fixes#110033.
a723194c1e