feat: fix UI freezes in ZIP and offline cache downloads

ZIP downloads (PlaylistDetail, Albums, NewReleases, RandomAlbums) now use
invoke('download_zip') via Rust streaming instead of fetch+blob+arrayBuffer,
eliminating JS heap saturation on large files. Progress shown in ZipDownloadOverlay.

Offline cache downloads (600+ songs) no longer freeze the UI: transient job
state moved to a separate non-persisted offlineJobStore, reducing localStorage
writes from ~1200 down to 2 for an entire download. Also adds playlist offline
toggle — clicking the cache button when already cached removes it from cache.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/de.ts

@@ -16,6 +16,7 @@ export const deTranslation = {
     expand: 'Sidebar einblenden',
     collapse: 'Sidebar ausblenden',
     downloadingTracks: '{{n}} Tracks werden gecacht…',
+    cancelDownload: 'Download abbrechen',
     offlineLibrary: 'Offline-Bibliothek',
     genres: 'Genres',
     playlists: 'Playlists',
@@ -823,6 +824,7 @@ export const deTranslation = {
     addSong: 'Zur Playlist hinzufügen',
     cacheOffline: 'Playlist offline speichern',
     offlineCached: 'Playlist gecacht',
+    removeOffline: 'Aus Offline-Cache entfernen',
     offlineDownloading: 'Wird gecacht… ({{done}}/{{total}} Alben)',
     publicLabel: 'Öffentlich',
     privateLabel: 'Privat',

src/locales/en.ts

@@ -17,6 +17,7 @@ export const enTranslation = {
     collapse: 'Collapse Sidebar',
 
     downloadingTracks: 'Caching {{n}} tracks…',
+    cancelDownload: 'Cancel download',
     offlineLibrary: 'Offline Library',
     genres: 'Genres',
     playlists: 'Playlists',
@@ -824,6 +825,7 @@ export const enTranslation = {
     addSong: 'Add to playlist',
     cacheOffline: 'Cache playlist offline',
     offlineCached: 'Playlist cached',
+    removeOffline: 'Remove from offline cache',
     offlineDownloading: 'Caching… ({{done}}/{{total}} albums)',
     publicLabel: 'Public',
     privateLabel: 'Private',

src/locales/fr.ts

@@ -16,6 +16,7 @@ export const frTranslation = {
     expand: 'Développer la barre latérale',
     collapse: 'Réduire la barre latérale',
     downloadingTracks: '{{n}} pistes en cache…',
+    cancelDownload: 'Annuler le téléchargement',
     offlineLibrary: 'Bibliothèque hors ligne',
     genres: 'Genres',
     playlists: 'Playlists',
@@ -821,6 +822,7 @@ export const frTranslation = {
     addSong: 'Ajouter à la playlist',
     cacheOffline: 'Mettre la playlist hors ligne',
     offlineCached: 'Playlist en cache',
+    removeOffline: 'Retirer du cache hors ligne',
     offlineDownloading: 'En cache… ({{done}}/{{total}} albums)',
     publicLabel: 'Publique',
     privateLabel: 'Privée',

src/locales/nb.ts

@@ -16,6 +16,7 @@ export const nbTranslation = {
     expand: 'Utvid sidefelt',
     collapse: 'Skjul sidefelt',
     downloadingTracks: 'Bufre {{n}} spor…',
+    cancelDownload: 'Avbryt nedlasting',
     offlineLibrary: 'Frakoblet bibliotek',
     genres: 'Sjangere',
     playlists: 'Spillelister',
@@ -820,6 +821,7 @@ export const nbTranslation = {
     addSong: 'Legg til i spilleliste',
     cacheOffline: 'Bufre spilleliste offline',
     offlineCached: 'Spilleliste bufret',
+    removeOffline: 'Fjern fra offline-buffer',
     offlineDownloading: 'Bufre… ({{done}}/{{total}} album)',
     publicLabel: 'Offentlig',
     privateLabel: 'Privat',

src/locales/nl.ts

@@ -16,6 +16,7 @@ export const nlTranslation = {
     expand: 'Zijbalk uitklappen',
     collapse: 'Zijbalk inklappen',
     downloadingTracks: '{{n}} nummers worden gecached…',
+    cancelDownload: 'Download annuleren',
     offlineLibrary: 'Offline bibliotheek',
     genres: 'Genres',
     playlists: 'Playlists',
@@ -821,6 +822,7 @@ export const nlTranslation = {
     addSong: 'Toevoegen aan playlist',
     cacheOffline: 'Playlist offline opslaan',
     offlineCached: 'Playlist gecached',
+    removeOffline: 'Verwijder uit offline cache',
     offlineDownloading: 'Cachen… ({{done}}/{{total}} albums)',
     publicLabel: 'Openbaar',
     privateLabel: 'Privé',

src/locales/ru.ts

@@ -17,6 +17,7 @@ export const ruTranslation = {
     expand: 'Развернуть боковую панель',
     collapse: 'Свернуть боковую панель',
     downloadingTracks: 'Кэширование {{n}} треков…',
+    cancelDownload: 'Отменить загрузку',
     offlineLibrary: 'Офлайн-библиотека',
     genres: 'Жанры',
     playlists: 'Плейлисты',
@@ -878,6 +879,7 @@ export const ruTranslation = {
     addSong: 'В плейлист',
     cacheOffline: 'Сохранить плейлист офлайн',
     offlineCached: 'Плейлист сохранён',
+    removeOffline: 'Удалить из офлайн-кэша',
     offlineDownloading: 'Кэширование… ({{done}} из {{total}} альбомов)',
     publicLabel: 'Публичный',
     privateLabel: 'Личный',

src/locales/zh.ts

@@ -16,6 +16,7 @@ export const zhTranslation = {
     expand: '展开侧边栏',
     collapse: '收起侧边栏',
     downloadingTracks: '正在缓存 {{n}} 首歌曲…',
+    cancelDownload: '取消下载',
     offlineLibrary: '离线音乐库',
     genres: '流派',
     playlists: '播放列表',
@@ -817,6 +818,7 @@ export const zhTranslation = {
     addSong: '添加到播放列表',
     cacheOffline: '离线缓存播放列表',
     offlineCached: '播放列表已缓存',
+    removeOffline: '从离线缓存中移除',
     offlineDownloading: '正在缓存… ({{done}}/{{total}} 张专辑)',
     publicLabel: '公开',
     privateLabel: '私有',