feat(db): add M6a library-list + artist-tracks queries

Appends ListArtistsAlphaWithCovers, ListAlbumsAlphaWithArtist,
CountAlbums, and ListArtistTracksForUser queries; regenerates sqlc.

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

internal/db/dbq/artists.sql.go

@@ -169,6 +169,69 @@ func (q *Queries) ListArtistsAlpha(ctx context.Context, arg ListArtistsAlphaPara
 	return items, nil
 }
 
+const listArtistsAlphaWithCovers = `-- name: ListArtistsAlphaWithCovers :many
+SELECT artists.id, artists.name, artists.sort_name, artists.mbid, artists.created_at, artists.updated_at,
+       cov.id AS cover_album_id,
+       cnt.album_count::bigint AS album_count
+FROM artists
+LEFT JOIN LATERAL (
+    SELECT id FROM albums
+    WHERE artist_id = artists.id AND cover_art_path IS NOT NULL
+    ORDER BY created_at DESC LIMIT 1
+) cov ON true
+LEFT JOIN LATERAL (
+    SELECT count(*) AS album_count
+    FROM albums WHERE artist_id = artists.id
+) cnt ON true
+ORDER BY artists.sort_name, artists.name, artists.id
+LIMIT $1 OFFSET $2
+`
+
+type ListArtistsAlphaWithCoversParams struct {
+	Limit  int32
+	Offset int32
+}
+
+type ListArtistsAlphaWithCoversRow struct {
+	Artist       Artist
+	CoverAlbumID pgtype.UUID
+	AlbumCount   int64
+}
+
+// M6a: alpha-sorted artist list with derived cover_album_id (most-recent
+// album whose cover_art_path is set). Replaces ListArtistsAlpha for the
+// /api/artists?sort=alpha branch — the new column is appended, so the
+// alpha branch is purely additive on the wire. album_count is computed
+// in the same query to drop the old N+1 in handleListArtists.
+func (q *Queries) ListArtistsAlphaWithCovers(ctx context.Context, arg ListArtistsAlphaWithCoversParams) ([]ListArtistsAlphaWithCoversRow, error) {
+	rows, err := q.db.Query(ctx, listArtistsAlphaWithCovers, arg.Limit, arg.Offset)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListArtistsAlphaWithCoversRow
+	for rows.Next() {
+		var i ListArtistsAlphaWithCoversRow
+		if err := rows.Scan(
+			&i.Artist.ID,
+			&i.Artist.Name,
+			&i.Artist.SortName,
+			&i.Artist.Mbid,
+			&i.Artist.CreatedAt,
+			&i.Artist.UpdatedAt,
+			&i.CoverAlbumID,
+			&i.AlbumCount,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const listArtistsNewest = `-- name: ListArtistsNewest :many
 SELECT id, name, sort_name, mbid, created_at, updated_at FROM artists ORDER BY created_at DESC, id DESC LIMIT $1 OFFSET $2
 `