Add "Save Image" button in media viewer

[jocmp]

Discussed in #693

^{Originally posted by Offerel January 7, 2025}
When i click on a image in a article, the image open fullscreen, which is fine. I would like to be able to save the image from this screen to the device.

[PhilC813]

Adding a "Share" button would also be useful!

[jocmp]

"Save" and "Share" buttons are now available in the media viewer as of 2025.02.1106-dev.