fix(pr168): title→data-tooltip, i18n playlist toggle, cold-start playlist fetch

- Replace title= with data-tooltip on sidebar playlist expand button (CLAUDE.md)
- Replace hardcoded Spanish aria-label strings with i18n keys (sidebar.expandPlaylists / collapsePlaylists) across all 8 locales
- AddToPlaylistSubmenu now fetches playlists on first open if store is empty (regression fix)

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

src/locales/es.ts

@@ -27,6 +27,8 @@ export const esTranslation = {
     folderBrowser: 'Explorar Carpetas',
     libraryScope: 'Ámbito de biblioteca',
     allLibraries: 'Todas las bibliotecas',
+    expandPlaylists: 'Expandir listas',
+    collapsePlaylists: 'Colapsar listas',
   },
   home: {
     hero: 'Destacado',