[guiyanakuang]

Closes #5236

Summary

• Replace the after-the-fact animateScrollToItem(0) recovery with a SideEffect that runs before the new items are measured. If the list sits exactly at its start (firstVisibleItemIndex == 0 && firstVisibleItemScrollOffset == 0) when the newest item changes, it calls requestScrollToItem(0), which overrides LazyList's key-based anchoring for the next measure. There is no scroll animation left to be interrupted, so the newest item can no longer end up half off-screen.
• When the user has scrolled away, nothing is requested and the default key anchoring keeps the viewport where it is.
• Wrap each slot (spacer + card) in Row(Modifier.animateItem()), so a prepended paste fades in while the existing cards slide right (removals fade out).
• Reopening the window is unchanged: resetToTop() still uses index-based scrollToItem(0).

Test plan

• Search window at the start, copy new content: the new item appears fully at the front with the insertion animation
• Scrolled several screens in, copy new content: the visible items do not move
• Inserting while searching/filtering and deleting an item animate naturally