Are cooked shrimp shells edible?
This depends partially on the cooking technique and the shrimp variety/size (=> thickness of the shell).

If the shrimp is deep fried the shell can turn crispy and is super fun to eat. However, if boiled, the shells are chewy and extremely unpleasant - in this case you have to peel them.

I am not familiar with the spicy garlic shrimp, but you can just try if the shell is crunchy, is pleasant to eat, and does not require excessive painful chewing - go for it, if not return to your old practice of pealing it and just licking the flavoring of the shells.