STOCKTON — The altar in the front of the auditorium was a poignant reminder of why they were all there.It was a tribute to 20-year-old Brandon Harrison, Stockton’s latest shooting victim and the 41st homicide being investigated by the Stockton Police Department this year.About 100 people gathered Thursday for an all-day summit titled, “On the Front Lines: End Gun Violence” at the Stockton Memorial Civic Auditorium.