SHANGHAI/BEIJING (Reuters) – One of China’s biggest ever foreign policy successes will take concrete shape on Monday when delegates from 57 countries sign an agreement on the Asian Infrastructure Investment Bank (AIIB) in Beijing. The founding members of the China-backed AIIB will sign articles of agreement that decide each member’s share and the bank’s initial capital. The multilateral institution, seen as a rival to the Western-dominated World Bank and Asian Development Bank, was initially opposed by the United States but has attracted many prominent U.S.