feat(folder-browser): Miller columns directory navigation

New page /folders with macOS Finder-style column layout:
- getMusicDirectory / getMusicIndexes / getMusicFolders Subsonic API methods
- Root level uses getIndexes.view (music folder IDs are not getMusicDirectory IDs)
- Columns fill available width with flex: 1, min-width: 200px
- Auto-scroll to rightmost column on expand
- Cancelled-flag prevents stale state on fast navigation
- Clicking a track plays it in the context of the current column's tracks
- FolderOpen/Folder/Music icons, accent-colored selection, ellipsis truncation
- Hidden in sidebar by default (user can enable in Settings)
- i18n: EN DE FR NL NB ZH RU

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

src/locales/de.ts

@@ -21,6 +21,7 @@ export const deTranslation = {
     playlists: 'Playlists',
     mostPlayed: 'Meistgehört',
     radio: 'Internetradio',
+    folderBrowser: 'Ordner-Browser',
     libraryScope: 'Bibliotheksumfang',
     allLibraries: 'Alle Bibliotheken',
   },
@@ -880,5 +881,9 @@ export const deTranslation = {
     favorite: 'Zu Favoriten hinzufügen',
     unfavorite: 'Aus Favoriten entfernen',
     noFavorites: 'Keine Lieblingssender.',
-  }
+  },
+  folderBrowser: {
+    empty: 'Leerer Ordner',
+    error: 'Laden fehlgeschlagen',
+  },
 };

src/locales/en.ts

@@ -22,6 +22,7 @@ export const enTranslation = {
     playlists: 'Playlists',
     mostPlayed: 'Most Played',
     radio: 'Internet Radio',
+    folderBrowser: 'Folder Browser',
     libraryScope: 'Library scope',
     allLibraries: 'All libraries',
   },
@@ -881,5 +882,9 @@ export const enTranslation = {
     favorite: 'Add to favorites',
     unfavorite: 'Remove from favorites',
     noFavorites: 'No favorite stations.',
-  }
+  },
+  folderBrowser: {
+    empty: 'Empty folder',
+    error: 'Failed to load',
+  },
 };

src/locales/fr.ts

@@ -21,6 +21,7 @@ export const frTranslation = {
     playlists: 'Playlists',
     mostPlayed: 'Les plus joués',
     radio: 'Radio Internet',
+    folderBrowser: 'Explorateur de dossiers',
     libraryScope: 'Portée de la bibliothèque',
     allLibraries: 'Toutes les bibliothèques',
   },
@@ -875,5 +876,9 @@ export const frTranslation = {
     favorite: 'Ajouter aux favoris',
     unfavorite: 'Retirer des favoris',
     noFavorites: 'Aucune station favorite.',
-  }
+  },
+  folderBrowser: {
+    empty: 'Dossier vide',
+    error: 'Échec du chargement',
+  },
 };

src/locales/nb.ts

@@ -21,6 +21,7 @@ export const nbTranslation = {
     playlists: 'Spillelister',
     mostPlayed: 'Mest spilt',
     radio: 'Internettradio',
+    folderBrowser: 'Mappeleser',
     libraryScope: 'Biblioteksomfang',
     allLibraries: 'Alle biblioteker',
   },
@@ -874,5 +875,9 @@ export const nbTranslation = {
     favorite: 'Legg til i favoritter',
     unfavorite: 'Fjern fra favoritter',
     noFavorites: 'Ingen favorittstasjoner.',
-  }
+  },
+  folderBrowser: {
+    empty: 'Tom mappe',
+    error: 'Kunne ikke laste',
+  },
 };

src/locales/nl.ts

@@ -21,6 +21,7 @@ export const nlTranslation = {
     playlists: 'Playlists',
     mostPlayed: 'Meest gespeeld',
     radio: 'Internetradio',
+    folderBrowser: 'Mappenverkenner',
     libraryScope: 'Bibliotheekbereik',
     allLibraries: 'Alle bibliotheken',
   },
@@ -875,5 +876,9 @@ export const nlTranslation = {
     favorite: 'Toevoegen aan favorieten',
     unfavorite: 'Verwijderen uit favorieten',
     noFavorites: 'Geen favoriete stations.',
-  }
+  },
+  folderBrowser: {
+    empty: 'Lege map',
+    error: 'Laden mislukt',
+  },
 };

src/locales/ru.ts

@@ -22,6 +22,7 @@ export const ruTranslation = {
     playlists: 'Плейлисты',
     mostPlayed: 'Часто слушаемое',
     radio: 'Онлайн-радио',
+    folderBrowser: 'Браузер папок',
     libraryScope: 'Область медиатеки',
     allLibraries: 'Все библиотеки',
   },
@@ -933,4 +934,8 @@ export const ruTranslation = {
     unfavorite: 'Убрать из избранного',
     noFavorites: 'Избранных станций нет.',
   },
+  folderBrowser: {
+    empty: 'Папка пуста',
+    error: 'Ошибка загрузки',
+  },
 };

src/locales/zh.ts

@@ -21,6 +21,7 @@ export const zhTranslation = {
     playlists: '播放列表',
     mostPlayed: '最常播放',
     radio: '网络电台',
+    folderBrowser: '文件夹浏览器',
     libraryScope: '资料库范围',
     allLibraries: '所有资料库',
   },
@@ -871,5 +872,9 @@ export const zhTranslation = {
     favorite: '添加到收藏',
     unfavorite: '从收藏移除',
     noFavorites: '没有收藏的电台。',
-  }
+  },
+  folderBrowser: {
+    empty: '空文件夹',
+    error: '加载失败',
+  },
 };