CALAIS, France — Refugees have traveled thousands of miles to start a new life outside war-torn Syria, but the hardest part of their journey may be crossing the English Channel. For decades, the French port of Calais has been the last stop for undocumented immigrants on their clandestine journey to Britain. Hundreds come here to wait their chance. In recent months, Syrians started arriving. Many of them have not yet been able to leave.