feat(web): update nav (Home/Artists/Albums); retire ArtistRow

Add Artists and Albums nav entries, rename root label from Library to
Home. Migrate all three ArtistRow call sites (search, search/artists,
library/liked) to ArtistCard with grid wrapper; delete ArtistRow
component and its test.

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

web/src/lib/components/Shell.svelte

@@ -22,7 +22,9 @@
   }
 
   const navItems = [
-    { href: '/',                label: 'Library' },
+    { href: '/',                label: 'Home' },
+    { href: '/library/artists', label: 'Artists' },
+    { href: '/library/albums',  label: 'Albums' },
     { href: '/library/liked',   label: 'Liked' },
     { href: '/library/hidden',  label: 'Hidden' },
     { href: '/search',          label: 'Search' },