Wire horizontal swipe into the mobile tap-zone overlay (single mode only,
so continuous mode keeps native vertical scroll). A leftward swipe past the
threshold turns to the next page, rightward to the previous; a mostly-
vertical drag is ignored so panning a tall page never turns it. The gesture
suppresses the synthesized zone tap so it doesn't double-fire. Swipe
classification is a pure, unit-tested helper; e2e drives real touch pointer
events for horizontal (both directions) and vertical cases.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>