There’s a black cloud hovering over Heinz Field, and it sure isn’t carrying a bunch of Terrible Towels. All the black shirts in the stands on Sunday afternoon drove home worried and stayed worried. One rough loss was followed by another with the news that center Maurkice Pouncey will be gone for the season after suffering a knee injury. The organization was excited that David DeCastro, the top draft pick who missed much of his rookie season in 2012, was back on the interior of the offensive line; now, though, that unit won’t be at full strength in 2013, either. This franchise always fights back; let’s see how Six-burgh responds.