Mariona Caldentey’s 93rd-minute penalty delivered a win and a hefty dose of relief to fans bouncing behind the goal in the North Bank after the ball hit the back of the net, but Arsenal’s narrow defeat of HB Køge in their Champions League opener left more questions unanswered than answered for the struggling Gunners. Manager Renée Slegers’ puffed cheeks said it all when the full-time whistle went. If it had been revealed on the final whistle that a forcefield surrounded the opposition goal at M…