fix: use maintained screenshots in AppStream metainfo

Replace the 2024 main window screenshots, which show an outdated user
interface and are no longer used by the documentation, with the signal
and image screenshots generated with the documentation screenshots.

Assisted-by: Claude Opus 5.5

Author: PierreRaybaut

com.datalab_platform.DataLab.metainfo.xml

@@ -63,11 +63,11 @@
     </screenshot>
     <screenshot>
       <caption>Signal panel with a chain of processing steps</caption>
-      <image>https://raw.githubusercontent.com/DataLab-Platform/DataLab/main/doc/images/DataLab-Screenshot-Signal.png</image>
+      <image>https://raw.githubusercontent.com/DataLab-Platform/DataLab/main/doc/images/shots/s_beautiful.en.png</image>
     </screenshot>
     <screenshot>
-      <caption>Image panel with the contrast adjustment tool</caption>
-      <image>https://raw.githubusercontent.com/DataLab-Platform/DataLab/main/doc/images/DataLab-Screenshot-Image.png</image>
+      <caption>Image panel with a chain of processing steps and the contrast adjustment tool</caption>
+      <image>https://raw.githubusercontent.com/DataLab-Platform/DataLab/main/doc/images/shots/i_beautiful.en.png</image>
     </screenshot>
   </screenshots>