The future of public transportation in New York City is taking shape on the bayous of Louisiana and Alabama. Shipyard workers in the two states are scrambling to finish the city’s new ferry fleet in time for a launch this summer, just a little more than a year after it was first proposed. The city is making a $335 million bet that the service will attract millions of passengers traveling between Manhattan and waterfront neighborhoods in Brooklyn, Queens and the Bronx that are now a distant walk from overcrowded subways.