The dozens of cargo ships anchored off the coast of Southern California last summer painted the picture of a robust economy, but behind the stranded armada waiting to unload its cargos was a story of supply-chain chaos and a damaging trade imbalance. Experts say the logjam experienced at the ports of Los Angeles and Long Beach may be a prelude to a deeper crisis that could affect all West Coast ports in coming months and years, including the Port of Oakland.