You need a disc specific front hub. There is no easy way to add a disc brake rotor to a hub that isn't designed for one.
While there's work-arounds, it's far better to keep to the same brand for shifters and derailleurs. Discussions of which brand is best should more appropriately take place in the politics and religion forum.
I gotta tell you, a super light year round commuter bike doesn't make a lot of sense to me. If it was my bike I'd be looking more for reliability and EZ maintenance.