Tokyo stocks ended flat Monday amid a cautious mood as Japan’s lower house was set to hold a runoff vote to choose the prime minister for the first time in three decades. The 225-issue Nikkei Stock Average ended up 32.95 points, or 0.08 percent, from Friday at 39,533.32. The broader Topix index finished 2.47 points, or 0.09 percent, lower at 2,739.68. On the top-tier Prime Market, gainers were led by nonferrous metal and rubber product issues, while top decliners were chemical and oil and coal product issues. The U.S. dollar briefly strengthened to the upper 153 yen range in Tokyo, as the U.S….