That’s one hell of a markup. Whoever moves into NYC Mayor-elect Zohran Mamdani’s rent-stabilized apartment in Queens will be shelling out an extra $800 — or 35% — more per month than what the socialist “nepo baby” did, The Post has learned. The Astoria apartment — which has quietly attracted interest from potential tenants for the past few weeks — is now commanding $3,100 per month while still remaining rent stabilized, sources said. Mamdani — who’ll be moving into Gracie Mansion with his “aloof” artist wife Rama Duwaji sometime after being sworn in Jan. 1 — caught a break during...