fix: every library album is matched to MusicBrainz before it is listed, by its tags, its artist's discography or a search, and checked against its tracks (M502 #5569)

The one-time listing took only albums whose tags already named their
release group and artist, and left 340 off the list. The rest are now
matched: the release their tags name, else the artist's release groups
called what the album is called, else a MusicBrainz search by artist and
title. A group found by name is taken only when its tracks agree with the
album's (by disc and number, then title; length and title, or recording),
so a partial copy still matches and a same-titled other album does not.

library_album_matches records each album the listing decided, listed or
unmatched with why, so an album taken off the list is never re-listed. The
albums no match was found for are named on the Held tab. Album rows with
no tracks are no longer counted.

The length and title checks move from the importer to release, shared by
both.

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

internal/api/admin_wanted.go

@@ -91,13 +91,24 @@ type wantsPage struct {
 }
 
 // libraryListingView: whether the library's albums are all on the list
-// yet, and how many could not be listed (nothing names them to
-// MusicBrainz).
+// yet, and which could not be matched to MusicBrainz (#5569). Unmatched is
+// filled on the first page of the held list only.
 type libraryListingView struct {
-	ListedAt *string `json:"listed_at"`
-	Unlisted int32   `json:"unlisted"`
+	ListedAt  *string              `json:"listed_at"`
+	Unlisted  int32                `json:"unlisted"`
+	Unmatched []unmatchedAlbumView `json:"unmatched"`
 }
 
+type unmatchedAlbumView struct {
+	AlbumID string `json:"album_id"`
+	Title   string `json:"title"`
+	Artist  string `json:"artist"`
+	Detail  string `json:"detail"`
+}
+
+// unmatchedShown is how many unmatched albums the held list names.
+const unmatchedShown = 200
+
 const wantsPageSize = 50
 
 // handleListWants implements GET /api/admin/wanted?state=wanted|missing|held&offset=.
@@ -137,10 +148,23 @@ func (h *handlers) handleListWants(w http.ResponseWriter, r *http.Request) {
 		Counts: wantCounts{Wanted: counts.Wanted, Missing: counts.Missing, Held: counts.Held, Following: counts.Following,
 			Activity: counts.Activity, Attention: counts.Attention, Blocked: counts.Blocked},
 	}
+	out.Library.Unmatched = []unmatchedAlbumView{}
 	if listing.LibraryListedAt.Valid {
 		at := formatTimestamp(listing.LibraryListedAt)
 		out.Library.ListedAt = &at
 	}
+	if state == "held" && offset == 0 && listing.LibraryUnlisted > 0 {
+		unmatched, err := q.ListUnmatchedLibraryAlbums(r.Context(), unmatchedShown)
+		if err != nil {
+			writeErrWithLog(w, h.logger, "admin wanted: unmatched albums", apierror.Internal(err))
+			return
+		}
+		for _, u := range unmatched {
+			out.Library.Unmatched = append(out.Library.Unmatched, unmatchedAlbumView{
+				AlbumID: uuidToString(u.AlbumID), Title: u.Title, Artist: u.ArtistName, Detail: u.Detail,
+			})
+		}
+	}
 	switch state {
 	case "missing":
 		out.Total = counts.Missing