feat: slected after buy

internal/economy/avatar.go

@@ -99,6 +99,11 @@ func (s *Service) BuyAvatar(ctx context.Context, userID int64, avatarID string)
 		`INSERT INTO user_avatars (user_id, avatar_id) VALUES (?, ?)`, userID, avatarID); err != nil {
 		return err
 	}
+	// خرید = مالکیت + انتخابِ خودکار.
+	if _, err := tx.ExecContext(ctx,
+		`UPDATE users SET selected_avatar = ? WHERE id = ?`, avatarID, userID); err != nil {
+		return err
+	}
 	return tx.Commit()
 }