Feature Request: Close a gallery by clicking on the background

### Impacted plugin

Jetpack

### What

Hi, Could you add the option to close a Jetpack gallery by clicking on the black/white background (depending on the settings) and not only on the little cross ? For example, like Woocommerce (with Strorefront theme) when we look a photo of a product. PS. Some users doesn't know that the key “Escape” can close a gallery (or a lightbox).

### How

_No response_

No files or tests are identified in the issue. Locate Jetpack's gallery or lightbox entry point and its existing close-button handling first, then verify that clicking the configured background closes the gallery without breaking image clicks or Escape-key behavior.

Written by the indexing model from the issue text.