add library filter, drop folders page

src/components/layout/AppHeader.tsx

@@ -33,7 +33,6 @@ const TOP_LEVEL_PATHS = new Set([
   '/',
   '/movies',
   '/shows',
-  '/folders',
   '/playlists',
   '/music',
   '/search',
@@ -45,7 +44,6 @@ function pageTitleFor(pathname: string): string {
   if (pathname === '/') return 'Home'
   if (pathname === '/movies') return 'Movies'
   if (pathname === '/shows') return 'TV Shows'
-  if (pathname === '/folders') return 'Folders'
   if (pathname === '/playlists') return 'Playlists'
   if (pathname === '/music') return 'Music'
   if (pathname === '/search') return 'Search'