fix(pr-review): address review findings for music folder filter

- Sidebar.tsx: title={} → data-tooltip + data-tooltip-pos="right" on
  scope subtitle (CLAUDE.md rule: never use native title= for tooltips)

- authStore.ts: merge two set() calls in setMusicFolders into one atomic
  update — avoids double render on folder list arrival

- locales (all 7): remove dead libraryScopeHint key (defined but never
  rendered in any component)

- Genres.tsx: remove musicLibraryFilterVersion from effect deps —
  getGenres is intentionally not folder-scoped, re-fetching on filter
  change was a no-op waste

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

src/locales/nl.ts

@@ -24,7 +24,6 @@ export const nlTranslation = {
     playlists: 'Playlists',
     radio: 'Internetradio',
     libraryScope: 'Bibliotheekbereik',
-    libraryScopeHint: 'Doorzoek de hele servercatalogus of één mediabibliotheek.',
     allLibraries: 'Alle bibliotheken',
   },
   home: {