I'm looking for suggestions on what to put in there for entertainment so they can find joy inside this area all day.
I know I still need to add a roof to the run.
I've got some big branches in my run. Chickens perch on them run under them, etc. Plus a bed of deep litter underneath.
You could still let them out for a supervised hour or so every day, long enough so they could eat some grass but not long enough to cause mass destruction.
Chickens to be happy just need their instincts met.
Provide a few places to perch during the day to rest and preen.
Provide a good place to dust bathe. I dug them a hole about a foot deep, three feet long and added a bag of play sand. This is were they do 99% of their dirt baths.
Add your lawns clippings, leaves maybe a bale of straw thrown about the run. As you know chickens spend a lot of time scratching and looking for things to eat. By adding these things it gives them that opportunity to satisfy that need to scratch around.
When I go out to lock my birds up at night I take scratch grain (not much) and throw it about the run and then take the rake ( I leave it propped next to the gate) and cover it up. My birds will spend hours during the day scratching through the litter looking for it. It has worked well for me years to keep their boredom down.
Like the one poster said it does not have to be the end to their "free range" time. I let mine out a couple times a week to eat fresh grass etc. I do so about an hour before they usually put themselves to roost. I then stand guard with a garden hose and when they get to close to a flower bed or their favorite place to destroy the rock around my garden pond I squirt it in their direction and they head the other way. My garden is fenced (has to be because of all the rabbits) so they can't get in there.