## 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
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