Helmets with dedicated mounting system for lights, cameras etc.?
The only helmets with built-in light mounts I know of are by Bell, which can mount the Blackburn Flea. I don't know if any of them are full-face. The Flea is pretty useless for offroad riding, it's too dim.

Lights usually mount up with velcro straps through the vents. When I was racing my MTB after dark Ay-Ups were common - small, extremely bright, and a remote battery pack that can be put somewhere comfortable. Not cheap though. Most lights with separate battery packs should be able to mount to a helmet. Check out Bikeradar or something for options.