fix: Fix AI chat not opening on home page (#11514)
## Summary
- Moves responsive visibility classes from `Portal.Root` to inner
`<div>` element
- `Portal.Root` from `radix-ui` doesn't support `className` prop, so the
classes were being ignored
The AI chat wasn't opening because the `hidden md:block` classes on
`Portal.Root` had no effect, causing the portal content to not render
properly on desktop.
