ol-carousel touch gestures and swipe physic refinements - #13101

Touch swipes were unreliable: starting a vertical page scroll on the
carousel could fire a page navigation (pointercancel was handled as a
release), horizontal swipes scrolled the page underneath, and after the
first page transition the swipe surface went dead on iOS (the
pointerdown listener lived on the translated track).

- Resolve gesture ownership with an axis lock (8px dead zone, 2:1
  horizontal bias) and preventDefault page scroll once locked
- Treat pointercancel as an abort that springs home, never a navigation
- Move gesture listeners to the untransformed viewport so the whole
  surface stays swipeable on every page
- Smooth velocity (EMA over >=4ms windows, capped, stale samples
  discarded) so release momentum is stable
- Land long drags on the nearest page; momentum carries at most one
  page beyond it

Adds a jest suite covering the gesture state machine.

ol-carousel refinements:
- Deepen the cover lookahead from one page to two on the first hover or
  keyboard focus, so fast page-flipping stays ahead of the loaded range.
  Skipped on data-saver / 2g connections; fires at most once.
- Add arrow-key / Home / End navigation to the page-indicator tablist
  with a roving tabindex (APG Tabs pattern), plus tests.
- Regenerate custom-elements.json to match.

…ements

Add discrete wheel-based paging: a horizontal trackpad swipe (wheel
events with deltaX) flips one page per gesture, reusing the existing
spring. Only claims horizontal-dominant intent, so vertical scroll and
plain mouse wheels pass through; preventDefault owns the gesture and
suppresses macOS history back/forward swipe. Momentum tail is swallowed
so one physical swipe pages once.

Adds 7 unit tests covering direction, vertical pass-through, threshold,
momentum lock, gesture-end re-arm, and line-mode normalization.