feat: Collection › Unmatched lists the library albums no MusicBrainz album matched, each matched by hand from a search or a link, or left off (M502 #5579)

Like Lidarr's Unmapped Files. A local band's album, which MusicBrainz will
never have, is left off: never matched again and not counted. A re-tagged
album is matched again on the next listing. The Collection's verdict now
says when library albums need matching.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/lib/components/wanted/CollectionRail.svelte

@@ -5,7 +5,9 @@
   // The Collection's sections, down the left like Lidarr's (#5572): the
   // catalogue of artists first, then the sections that show state. On a
   // narrow screen the rail runs across the top. Activity carries a second,
-  // accented count when downloads are waiting on a person.
+  // accented count when downloads are waiting on a person. Unmatched, like
+  // Lidarr's Unmapped Files, holds the library albums no MusicBrainz album
+  // matched (#5579).
 
   let { counts }: { counts?: WantCounts } = $props();
 
@@ -17,7 +19,8 @@
     { href: '/collection/missing', label: 'Missing files', count: counts?.missing },
     { href: '/collection/activity', label: 'Activity', count: counts?.activity, attention: counts?.attention },
     { href: '/collection/following', label: 'Following', count: counts?.following },
-    { href: '/collection/blocked', label: 'Blocked', count: counts?.blocked }
+    { href: '/collection/blocked', label: 'Blocked', count: counts?.blocked },
+    { href: '/collection/unmatched', label: 'Unmatched', count: counts?.unmatched }
   ]);
 
   // An artist's page belongs to the catalogue.