The 12-year-old Brooklyn girl killed in a Brooklyn subway surfing incident had posted terrifying daredevil TikTok videos — including one where she lay on train tracks — in the weeks leading up to her tragic death, The Post has learned. The videos were revealed as young Zemfira Mukhtarov’s mother said her pre-teen daughter was obsessed with pulling off the social media stunts despite her parents’ pleading, and had snuck out in the middle of the night Saturday before she was killed. “I always