Global investors are bracing for another hair-raising ride, after a week of frantic and at times disorderly trading. The Dow industrials have dropped seven straight days entering trading Monday, posting their steepest weekly decline since the financial crisis. Their 14% pullback since Feb. 12 places the longest-ever U.S. stock rally in jeopardy of falling into a “bear market,” marking a 20% decline from a recent high. The…