This fixes a minor issue in the website editor test suite by ensuring test page content is properly cleaned up after a save test. It helps keep automated testing reliable and prevents one test from affecting later checks, with no direct impact on end users.

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Removing an image from an image wall now deletes only the selected image instead of sometimes removing two. The image add helper also reappears when the last image is removed, making gallery editing more reliable for website editors.

* On image remove was removing two images instead of one -> fixed
* Reactivate the image adder helper if you manually remove the last image

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Bug report :

[QSM] Images wall snippet -> Add images -> click on one -> Delete via the trash icon button on the overlay -> Sometimes (most of the time) delete 2 images instead of the selected one

This fix ensures that when a website editor adds a background video, any previous background image is properly cleared. It helps prevent unwanted visual overlap or outdated imagery from appearing on published pages.

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