Kyle Richards, Mauricio Umansky Step Out Together for Daughter's Birthday

Here's a rare sight these days ... Kyle Richards and Mauricio Umansky hitting the town together -- but it's not a sign they've smoothed out their marital issues, it's just that they're great parents. The separated couple publicly reunited in Bel Air to celebrate their daughter Portia's 16th birthday. The fam left a restaurant together Thursday night -- Mauricio was carrying what seemed like a gift or cake box ...…