Kurdish forces geared up Monday for an assault on a prison in northeast Syria that so-called Islamic State group fighters stormed last week, sparking fears for the fate of hundreds of underage detainees. IS fighters on Thursday rammed two explosives-packed vehicles into the Kurdish-run Ghwayran prison to launch a brazen jailbreak operation that has plunged the city of Al-Hasaka into chaos. The attack is the group’s biggest since their once sprawling self-styled “caliphate” was defeated in 2019. It has already killed more than 150 people, most of them jihadists. Fighting drove up to 45,000 resi…