Notifications page switches code style without explanation (plain JS to JSX)

## Description
The Notifications feature page shows two code examples that use inconsistent
styles without explaining why.

- The basic `snap_notify` example (Step 2) uses plain JavaScript.
- The "Expanded view" example immediately below uses JSX components
(``, ``) with no explanation that JSX is required for
expanded view content.

This is confusing for new developers who don't understand why the two
examples look so different.

## Page URL
https://docs.metamask.io/snaps/features/notifications/

## Suggested fix
Add a brief note before the expanded view example clarifying that the
`content` field requires JSX (or the functions-based equivalent),
and link to the Custom UI docs for context.

Open the Notifications feature page at the provided URL and compare the Step 2 and Expanded view examples. Add the requested explanation that expanded-view content requires JSX or the functions-based equivalent, link to the Custom UI docs, and verify the rendered documentation is clear.

Written by the indexing model from the issue text.