feat: Updated screensaver image mode fetches random images (#2430)

BREAKING CHANGE: The `screensaver` image mode now shows a random image
from [picsum.photos](picsum.photos) instead of the embedded default
image. If you previously set `image.mode: screensaver`, change it to
`image.mode: default` to restore the previous behavior.

src/localize/languages/de.json

@@ -133,8 +133,9 @@
         "entity": "Entität für Entitäts-Modus",
         "entity_parameters": "Abfrage-Parameter für Entitäts-basierende Photo URLs (z.B. width=1920&height=1080)",
         "modes": {
+          "default": "Standard-Eingebettetes Bild",
           "entity": "Entität mit entity_picture Attribut",
-          "screensaver": "Eingebettetes Bild für Bildschirmschoner"
+          "screensaver": "Zufälliges Bild"
         }
       },
       "media_action_conditions": {