Update `WikiMed Offline` (de) to support Android 15.

See issue https://github.com/kiwix/kiwix-android/issues/4270. As our Kiwix app now supports Android 15 so our custom app should also support Android 15.

**Folder Name:** [wikimedde](https://github.com/kiwix/kiwix-android-custom/tree/main/wikimedde)
**Package Name:** `org.kiwix.kiwixcustomwikimedde`


![Image](https://github.com/user-attachments/assets/03d8535a-5ce2-42af-b038-795b87243980)