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>

internal/api/api.go

@@ -252,6 +252,7 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 				// for, the artists it follows, and the release-type
 				// profiles that decide which of their releases count.
 				admin.Get("/wanted", h.handleListWants)
+				admin.Get("/wanted/artists", h.handleListWantArtists)
 				admin.Delete("/wanted/{id}", h.handleRemoveWant)
 				// Searching and grabbing (M502 #5521).
 				admin.Get("/acquisition/settings", h.handleGetSearchSettings)