Can I cook/eat milled barley malt?

Post mashing you've actually removed much of the nutritional portion of it and put that stuff in your wort. The primary component left then is all that fiber. Even using the unmashed malt for the normal human diet, its a very high fiber to nutrient ratio.

You can eat it but it is a lot of fibrous material to digest. Thoroughly cooking it will soften the husk for sure and make it easier to consume. Still its best to not eat a lot of it.

The best application then is to use it as a fiber booster in some other food items. Many people will add some of it to bread mixes. I have seen it applied to chili and stews at some brewpubs. (Again that wet application softening the husks making it easier to eat/digest). However, even in these applications we are talking about a cup of the spent mash, not an application for the whole mash.

You don't want to eat the husk. You can, but it's about like eating a wood toothpick. But we need husks in the mash as they work as the filter for lautering.

As for using a spent grain. After a mash you will spead it out very thin to dry, turning it often. Puting it on a screen with a fan below helps speed up the drying process. Wet spent grain can "spoil" pretty fast so drying quick is a must. Once dry you can then winnow to remove the husks, then use the grain for cereals, bars, or grind to flour.