CANBERRA — Australia and Vanuatu signed a sweeping economic and security agreement on Monday that bars the establishment of any foreign military base on the Pacific island. Vanuatu is at the center of strategic rivalry between China and US allies in the South Pacific, and Australia has expressed concern that Beijing is seeking a permanent security presence in the region.The agreement commits Australia to greater economic support for Vanuatu, whose largest external creditor is China, and it stops a foreign military power establishing a base there. “What this does do is to provide certainty for Australia that there will be…