* Restore combined diff scroll position using virtualized scroll anchors
Fixes scroll jumping and incorrect restoration in virtualized combined
diff views by tracking scroll position via a stable row anchor (key and
offset) rather than a fragile raw scrollTop.
- Track active row anchors across tab switches and component remounts
- Prevent programmatic scroll events from writing incorrect anchors
- Avoid redundant state updates and re-renders when focusing an
already focused group
* fix: address review findings
Jinjing