The U.N. refugee agency said Thursday that 1 million people have now fled Ukraine since Russia’s invasion less than a week ago, an exodus without precedent in this century for its speed. The tally from the U.N. High Commissioner for Refugees amounts to more than 2% of Ukraine’s population — which the World Bank counted at 44 million at the end of 2020 — on the move across borders in just seven days. The agency cautions that the outflows are far from finished: It has predicted that as many as 4 million people could eventually leave Ukraine, and even that projection could be revised upward. In a…