fix(render): align scrollToRowPosition from the row's actual offsetTop - #4930

scrollToRowPosition's center/bottom math derived the offset from the current
scrollTop, assuming scrollToRow had placed the target at the top of the
window. For rows that cannot sit at the top after the fill (e.g. near the
end of the list) this misaligned them — measured ~12px off for center.
Compute the alignment from the row's actual offsetTop instead, and sync
vDomScrollPosTop/Bottom afterwards so the next user scroll does not diff
against a stale tracker and jump (guarded for the basic renderer).

Adds a Playwright regression test asserting a near-bottom row lands within
6px of top/center/bottom.

…-to-row-position