batches: prevent overflow spill with margin again

Created by: courier-new

https://github.com/sourcegraph/sourcegraph/pull/26812 but better.

The important thing here is just having that <div> (or any display: block container) wrap the component with Page (which introduces the consistent vertical padding). This was explored in the previous PR: since the next nearest parent is a display: flex container, it otherwise eats the bottom margin. The <div> wrapper wasn't included on DotcomGettingStartedPage, hence the regression. This ensures all pages in the global area have that wrapper.