Mayor Zohran Mamdani and City Council Speaker Julie Menin managed Tuesday to agree on a budget for the year that starts July 1 with just hours to go. New Yorkers may wish they hadn’t bothered. For starters, the ginormous $126 billion plan is, per city Comptroller Mark Levine, essentially unsound — as it relies on one-shots, fiscal gimmicks, phony savings and, basically, chewing gum to hold it together.