feat(immich): add prefetch and mobile data controls

Adds Immich image prefetch and a mobile data option to the UI.
Android now ships ImmichPrefetchWorker to fetch originals in the background.
Frontend and desktop code are updated to expose and persist new settings.
Translations cover the new labels and hints in multiple languages.

- Introduce ImmichPrefetchWorker for background prefetch
- Add allowMobileData and prefetchImmich UI controls
- Wire changes to desktop state and translations

plugins/src/desktop.rs

@@ -21,6 +21,8 @@ impl<R: Runtime> Wallpaper<R> {
             interval_minutes: 30,
             shuffle: true,
             lock_screen_only: true,
+            allow_mobile_data: false,
+            prefetch_immich: true,
             current_index: 0,
             current_id: Some("demo-0".into()),
             image_ids: vec!["demo-0".into(), "demo-1".into(), "demo-2".into()],
@@ -89,6 +91,8 @@ impl<R: Runtime> Wallpaper<R> {
             "enabled" => state.enabled = payload.value,
             "shuffle" => state.shuffle = payload.value,
             "lockScreenOnly" => state.lock_screen_only = payload.value,
+            "allowMobileData" => state.allow_mobile_data = payload.value,
+            "prefetchImmich" => state.prefetch_immich = payload.value,
             _ => {}
         };
         Ok(state)

plugins/src/models.rs

@@ -8,6 +8,8 @@ pub struct WallpaperState {
     pub interval_minutes: i32,
     pub shuffle: bool,
     pub lock_screen_only: bool,
+    pub allow_mobile_data: bool,
+    pub prefetch_immich: bool,
     pub current_index: usize,
     pub current_id: Option<String>,
     pub image_ids: Vec<String>,