Kim Kardashian is celebrating her nephew’s first birthday. Sharing a trio of photos on Instagram Friday where she spends time with Khloé Kardashian’s son Tatum, the SKIMS co-founder, 42, called her youngest nephew “such a smoosh.” “My baby Tatum Happy 1st Birthday! OMGGGG you are such a smoosh, the happiest baby boy of all time,” she wrote. “I can’t even …