feat: the Wanted view becomes Collection, shaped like Lidarr: an artist catalogue first, the state sections down a left rail (M502 #5577)

The section opens on a catalogue of every artist on the list, A–Z with a
letter rail, each card showing how many of their albums are held. An artist
opens on their page: every album of theirs, held or not, with its status,
search, releases and tracks. Wanted, Missing files, Activity, Following and
Blocked sit down a left rail as the sections that show state; Held is gone,
the catalogue shows it. The section moves from /wanted to /collection.

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

web/src/routes/admin/requests/+page.svelte

@@ -146,7 +146,7 @@
     <h2 class="font-display text-2xl font-medium text-text-primary">Requests</h2>
     <p class="text-text-secondary">
       Approve or set aside what users have asked for. An approved album or track goes on the
-      <a href="/wanted" class="text-accent-fg hover:underline">wanted list</a>; an approved
+      <a href="/collection/wanted" class="text-accent-fg hover:underline">wanted list</a>; an approved
       artist is followed, wanting what they've released and what they release next.
     </p>
   </header>