Wikimedia providers don't provide images

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• This is not a feature request
• This is not an image-provider request
• I have searched the issuetracker if the issue is not already reported.

Describe the bug:
The Wikimedia providers don't provide an image anymore. Root cause seem to be a missing user agent header in the image request, which Wikimedia requires for all requests, see the robot policy at https://w.wiki/4wJS, and further https://foundation.wikimedia.org/wiki/Policy:Wikimedia_Foundation_User-Agent_Policy.
This policy exists since 2010, but the bug only appeared recently, so I assume there was a change in curl behavior with PHP 8, maybe the user agent was sent by default before and is now empty.

To Reproduce:
Steps to reproduce the behavior:

1. Set a Wikimedia provider in the Design settings

Expected behavior:
The image shows in the preview and as background after logoff

Server:

• Nextcloud version: 31.0.8
• Splash-App version: 3.1.0

Additional Information:
One can simulate the request with curl, e.g.: curl -H 'User-Agent:' "https://commons.wikimedia.org/w/api.php?action=query&generator=images&titles=Template:Potd/2025-09-03&prop=imageinfo&iiprop=url&format=json"

Trace the Wikimedia provider request from the Design settings and compare it with the curl example in the issue, paying particular attention to the User-Agent header and the Wikimedia API response. Done means Wikimedia images appear in the preview and as the logged-out background without violating Wikimedia's User-Agent policy.