Madrid surged to a standstill on Sunday morning as more than a million people crowded the capital’s streets and a landmark square for a fleeting look at Pope Leo XIV, who traveled to an open-air Mass set to become the biggest gathering of his week-long visit to Spain. Flags fluttered above the crowds and chants of “long live the pope” rang out as the pontiff rode in the popemobile along Madrid’s grand Paseo de la Castellana toward Cibeles Square, where he was scheduled to celebrate the Mass. As he entered the square, some in…