chore: improve web example large item jump

[PaulSenon]

For #409

Changes:

• refactored example-web/src/examples/PrependLargeItemsJumpExample.tsx that was scroll container only to:
  • useWindowScroll prop to share same page component for both window/container scroll mode
  • better layout (main content full height and sidebard with controls and logs)
  • added control preset for new broken case (seems like it's more sensitive to page size rather than item size since beta-41)
  • added url param persistence
• adde route example-web/src/router.tsx in sidebar for window version of the existing demo

AI disclaimer: This is mainly vibe coded