Russia is heading into 2026 with a familiar problem wearing a sharper edge: the oil revenues that bankroll its budget — and its war — are shrinking fast. According to Reuters calculations released Friday, Russia’s tax proceeds from crude oil production in January could fall to about 380 billion roubles ($4.7 billion), the lowest monthly take since late 2022. That would mark a 16% drop from December and a collapse of more than 50% compared with January last year. For a government that still leans heavily on oil income to fund military…