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/zh.ts

@@ -26,6 +26,8 @@ export const zhTranslation = {
     folderBrowser: '文件夹浏览器',
     libraryScope: '资料库范围',
     allLibraries: '所有资料库',
+    expandPlaylists: '展开播放列表',
+    collapsePlaylists: '收起播放列表',
   },
   home: {
     hero: '精选',