SEATTLE — The first offseason domino for the Storm fell when Sue Bird announced she’s returning to Seattle next season. In an Instagram post Friday morning, the 41-year-old veteran point guard put an end to months of speculation on whether the WNBA’s all-time assist leader would retire or return for her 19th season. Following a second-round loss in the WNBA playoffs, Bird was unsure about her future. After the 85-80 defeat to the Phoenix Mercury, she swapped jerseys with longtime friend Diana Taurasi at midcourt as the Angel of Arena fans chanted “one more year.” “When you have the fans cheer …