white clover...nice and low, pretty flowers,
bees love it...
The purslane would likely leave so much soil exposed - I bet it would look pretty sloppy after a wet spring. Maybe have a pathway somehow...for best shade-tolerant fruits in your area - black currants (leaves get nibbled way less than reds or whites at my place) gooseberries..jostaberries...even a hardy kiwi against that wall if it gets some sun. Russian comfrey too...that will get things super lush - as would some rhubarb. Have fun with that it will look amazing.