Fix duplicate download insert: handle NULL columns in download scan, check by torrent ID, enrich MonitorAlbum response, recover orphaned downloads on startup

internal/database/download_repository.go

@@ -16,8 +16,8 @@ type Download struct {
 	Quality      string
 	State        string
 	QbitHash     string
-	SavePath     string
-	ErrorMessage string
+	SavePath     *string
+	ErrorMessage *string
 	QueuedAt     time.Time
 	StartedAt    *time.Time
 	CompletedAt  *time.Time
@@ -107,6 +107,19 @@ func (r *DownloadRepository) GetByAlbumID(ctx context.Context, albumID string) (
 	return downloads, nil
 }
 
+func (r *DownloadRepository) GetActiveByTorrentID(ctx context.Context, torrentID string) (*Download, error) {
+	d := &Download{}
+	err := r.pool.QueryRow(ctx,
+		`SELECT id, torrent_id, album_id, format, quality, state, qbit_hash, save_path, error_message, queued_at, started_at, completed_at, created_at, updated_at
+		 FROM downloads WHERE torrent_id = $1 AND state NOT IN ('failed')
+		 ORDER BY created_at DESC LIMIT 1`, torrentID,
+	).Scan(&d.ID, &d.TorrentID, &d.AlbumID, &d.Format, &d.Quality, &d.State, &d.QbitHash, &d.SavePath, &d.ErrorMessage, &d.QueuedAt, &d.StartedAt, &d.CompletedAt, &d.CreatedAt, &d.UpdatedAt)
+	if err != nil {
+		return nil, fmt.Errorf("getting active download by torrent: %w", err)
+	}
+	return d, nil
+}
+
 func (r *DownloadRepository) GetActive(ctx context.Context) ([]*Download, error) {
 	rows, err := r.pool.Query(ctx,
 		`SELECT id, torrent_id, album_id, format, quality, state, qbit_hash, save_path, error_message, queued_at, started_at, completed_at, created_at, updated_at