Ben Soleimani, whose family has been in the rug business for four generations, is continuing his collaboration with Restoration Hardware, where he is now the company’s full-time rug designer and collector. The new items will debut online in April as part of the RH spring collection. Soleimani and Restoration Hardware first partnered on a 400-rug collection in 2011, when he was working at the Los Angeles branch of his London-based family’s company, Mansour, but this latest effort will introduce more than 3,500 …