feat: bulk multi-select + drag in PlaylistDetail, Favorites, and artist context menu (#157)

- PlaylistDetail: Ctrl/Cmd+Click enters select mode; bulk drag emits
  { type: 'songs', tracks } when ≥2 selected; filtered-view rows now
  also draggable as single songs
- Favorites songs: full multi-select system — Ctrl+Click, Shift+Click,
  header toggle-all checkbox, bulk-selected highlight, bulk drag to
  queue, bulk-bar with Add to Playlist + Clear
- ContextMenu: ArtistToPlaylistSubmenu resolves all artist album songs
  and forwards to AddToPlaylistSubmenu
- Locale: common.clearSelection + playlists.addSelected in all 7 locales

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

src/locales/ru.ts

@@ -377,6 +377,7 @@ export const ruTranslation = {
     filterNoGenres: 'Нет совпадений',
     filterClear: 'Сбросить',
     bulkSelected: 'Выбрано: {{count}}',
+    clearSelection: 'Сбросить выбор',
     bulkAddToPlaylist: 'В плейлист',
     bulkRemoveFromPlaylist: 'Убрать из плейлиста',
     bulkClear: 'Снять выделение',
@@ -958,6 +959,7 @@ export const ruTranslation = {
     titleBadge: 'Плейлист',
     refreshSuggestions: 'Обновить подборку',
     addSong: 'В плейлист',
+    addSelected: 'Добавить выбранные',
     cacheOffline: 'Сохранить плейлист офлайн',
     offlineCached: 'Плейлист сохранён',
     removeOffline: 'Удалить из офлайн-кэша',