Looking in the model file, I noticed a couple of things. For one thing, you probably want to give the fighter a nonzero mass, and MOI (pcs2 can calculate the moi). But I think what might be stopping your turret from firing is this:
$uvec:0, 0, -1
$fvec:0, 1, 0$special=subsystem
$fov=180
See if a line break between $fvec and $special fixes things.
Otherwise, you can check if the problem is with the beam or the model by temporarily substituting the beam with a normal turret weapon and seeing if that works.
Oh, and the collisionbox for your turret is really weird. You probably want to fix the centrepoint, otherwise the turret is going to have an enormous hitbox (calculated as 2x the radius of the turret, iirc). Also I noticed that the firepoint is offset in the x direction. Is that intentional?