DELHI — For over two months, Paramjit Singh, 48, a US green card holder battling a brain tumour and a heart condition, has been held in a detention centre by US immigration authorities.Singh, an IndianDELHI — For over two months, Paramjit Singh, 48, a US green card holder battling a brain tumour and a heart condition, has been held in a detention centre by US immigration authorities.Singh, an Indian