A great group of edible plants for shady areas are the waterleafs. Here in western WA we have Pacific waterleaf (Hydrophyllum tenuipes) but there are other waterleafs depending on where you live. Waterleafs do great in full shade and once established will spread and fill in. They're a great early spring green and can provide greens through the summer. Though later in the summer their leaves are tougher.
I've been transplanting Pacific waterleafs into my shady areas each fall/winter and I'm starting to get some nice patches in some deep shade areas.
I really like the flavor of the leaves and they can be eaten raw or cooked. You can also harvest younger
root tips which are supposed to have a flavor that is similar to Chinese beansprouts. My patches aren't big
enough for this harvest but I want to try it soon.