A week after a deadly knife attack at a city festival shook Germany, members of the public and national political leaders plan to gather on Sunday to mourn the victims. Three visitors to a festival celebrating the western city of Solingen’s 650th anniversary were stabbed to death and eight others were injured. A 26-year-old Syrian man who was living in a nearby refugee residence was arrested in the wake of the August 23 rampage. He is being held on suspicion of murder, suspected membership in the Islamic State terror group and other charges. President Frank-Walter Steinmeier and Chancellor Ola…