fix(dropdown): close popover when parent container scrolls

[faizkhairi]

Summary

• Close dropdown popover when any scrollable ancestor scrolls, preventing it from appearing above the sticky header
• Walks up the DOM tree to find all scrollable ancestors and attaches passive scroll listeners
• Uses existing setIsFocused(false) to close the popover (same mechanism as outside-click handler)

Related Issue

Closes #6026

Approach

Rather than adjusting z-index (which just masks the problem), this fix closes the popover when the user scrolls. This matches the behavior expected by the maintainer as described in the feedback on the earlier PR #6501.

Changes

File	Change
apps/frontend/src/components/Dropdown/components/SelectPopover/SelectPopover.tsx	Add useEffect to close popover on ancestor scroll

Implementation Detail

The useEffect runs when isOpen becomes true. It walks parentElement up the DOM from the floating-ui reference element, checking getComputedStyle for overflow: auto/scroll on each ancestor. Each scrollable ancestor gets a passive scroll listener. The window also gets a listener for page-level scroll. All listeners are removed in the effect cleanup when isOpen becomes false or the component unmounts.

Test Plan

• Open a dropdown in the form builder sidebar
• Scroll the sidebar -- dropdown should close
• Open a dropdown and scroll the page -- dropdown should close
• Verify dropdown still works normally (open, select, close on click outside)
• Verify no memory leaks (listeners cleaned up on unmount)