Completes the humanize suite:
- Clicks land on a jittered point inside the element's box (Fast/Human) instead
of its exact centre. `resolve_element_center` now also returns the element
width/height (box_model_dims); the CSS-selector path reports zero size → land
on centre (no jitter, no regression). Jitter is clamped to the inner box so the
click never misses.
- Wheel scrolls split into eased, jittered segments (humanize::scroll_segments,
unit-tested) instead of one instant jump.
- Drag follows the curved trajectory at Fast/Human (linear 10-step at Off).
Off is unchanged throughout. 9/9 unit tests; verified headless — jittered click
still lands (→ iana.org), segmented scroll moves the page.