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

src/App.tsx

@@ -1,10 +1,10 @@
 import { useEffect, useLayoutEffect, useMemo, useRef, useState } from "react";
-import { ArrowLeft, Check, ChevronRight, Cloud, CloudDownload, Crop, Home, Images, Languages, Link2Off, LockKeyhole, Plus, RotateCcw, RotateCw, Save, Server, Settings, Shuffle, Smartphone, Sparkles, Trash2 } from "lucide-react";
+import { ArrowLeft, Check, ChevronRight, Cloud, CloudDownload, Crop, Download, Home, Images, Languages, Link2Off, LockKeyhole, Plus, RotateCcw, RotateCw, Save, Server, Settings, Shuffle, Smartphone, Sparkles, Trash2, Wifi } from "lucide-react";
 import { applyWallpaper, connectImmich, deleteImages, disconnectImmich, getGallery, getImageIds, getImmichAlbums, getImmichAssets, getImmichConnection, getImmichImportProgress, getState, importImmichAssets, nextWallpaper, selectImages, setImageCrop, setIntervalMinutes, setSetting, type GalleryImage, type ImmichAlbum, type ImmichAsset, type ImmichConnection, type ImmichImportProgress, type WallpaperState } from "./native";
 import { initialLanguage, languageNames, languages, translations, type Language } from "./i18n-local";
 import { immichTranslations } from "./immich-i18n";
 
-const initial: WallpaperState = { imageCount: 0, enabled: false, intervalMinutes: 0, shuffle: true, lockScreenOnly: true, currentIndex: 0, currentId: null, imageIds: [], imageUrls: [] };
+const initial: WallpaperState = { imageCount: 0, enabled: false, intervalMinutes: 0, shuffle: true, lockScreenOnly: true, allowMobileData: false, prefetchImmich: true, currentIndex: 0, currentId: null, imageIds: [], imageUrls: [] };
 
 function Switch({ checked, onChange, label }: { checked: boolean; onChange: (value: boolean) => void; label: string }) {
   return <button className={`switch ${checked ? "on" : ""}`} role="switch" aria-checked={checked} aria-label={label} onClick={() => onChange(!checked)}><span /></button>;
@@ -107,13 +107,17 @@ export default function App() {
     finally { setGalleryLoading(false); }
   }
 
-  async function update(name: "shuffle" | "lockScreenOnly", value: boolean) {
+  async function update(name: "shuffle" | "lockScreenOnly" | "allowMobileData" | "prefetchImmich", value: boolean) {
+    const previous = state[name];
     setState(prev => ({ ...prev, [name]: value }));
     try {
       const saved = await setSetting(name, value);
       setState(saved);
       setNotice(t.settingSaved);
-    } catch { setNotice(t.androidOnly); }
+    } catch (error) {
+      setState(prev => ({ ...prev, [name]: previous }));
+      setNotice(String(error).replace(/^Error:\s*/, "") || t.androidOnly);
+    }
   }
 
   async function updateInterval(minutes: number) {
@@ -425,6 +429,10 @@ export default function App() {
           <div className="immich-title"><span><Cloud /></span><div><h3>{it.immich}</h3><p>{it.immichIntro}</p></div></div>
           {immichConnection.configured ? <>
             <div className="immich-connected"><strong>{it.connectedAs} {immichConnection.userName}</strong><span>{immichConnection.serverUrl}</span></div>
+            <SettingRow icon={<Download />} label={it.prefetchImmich} value={state.prefetchImmich} onChange={v => update("prefetchImmich", v)} />
+            <p className="immich-help">{it.prefetchImmichHint}</p>
+            <SettingRow icon={<Wifi />} label={it.allowMobileData} value={state.allowMobileData} onChange={v => update("allowMobileData", v)} />
+            <p className="immich-help">{it.allowMobileDataHint}</p>
             <button className="immich-open" onClick={openImmich} disabled={busy}><Images /> {it.openImmich} <ChevronRight /></button>
             <button className="immich-disconnect" onClick={removeImmichConnection} disabled={busy}><Link2Off /> {it.disconnect}</button>
           </> : <>