## Summary
Virtualize the FormDropdownMenu to only render visible items, fixing
slow dropdown performance on cloud.
## Changes
- Integrate `VirtualGrid` into `FormDropdownMenu` for virtualized
rendering
- Add computed properties for grid configuration per layout mode
(grid/list/list-small)
- Extend `VirtualGrid` slot to provide original item index for O(1)
lookups
- Change container from `max-h-[640px]` to fixed `h-[640px]` for proper
virtualization
## Review Focus
- VirtualGrid integration within the popover context
- Layout mode switching with `:key="layoutMode"` to force re-render
- Grid style computed properties match original Tailwind classes
┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8476-perf-virtualize-FormDropdownMenu-to-reduce-DOM-nodes-and-image-requests-2f86d73d365081b3a79dd5e0b84df944)
by [Unito](https://www.unito.io)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Dropdowns now render with a virtualized grid/list (stable indexes,
responsive sizing) and show an empty-state icon when no items exist.
* **Bug Fixes**
* Reduced layout shift and rendering glitches with improved
spacer/scroll calculations and more reliable media measurement.
* **Style**
* Simplified media rendering (standard img/video), unified item visuals
and hover/background behavior.
* **Tests**
* Added unit and end-to-end tests for virtualization, indexing, layouts,
dynamic updates, and empty states.
* **Breaking Changes**
* Dropdown item/selection shapes and related component props/events were
updated (adapter changes may be required).
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
---------
Co-authored-by: GitHub Action <action@github.com>
## Summary
Add `maxColumns` prop to VirtualGrid for responsive column capping.
## Changes
- **VirtualGrid**: Add `maxColumns` prop to cap grid columns; refactor
inline styles to Tailwind classes; extract spacer height computation to
helper function
- **AssetGrid**: Use `useBreakpoints` to set responsive `maxColumns`
(1-5 based on Tailwind breakpoints)
## Review Focus
- `maxColumns` behavior when `Infinity` vs finite: does
`gridTemplateColumns` override work correctly?
- Tailwind scrollbar classes replacing scoped CSS
