Officer followed, then struggled with, then shot and killed emotionally disturbed man; district court dismissed § 1983 claim and negligence claim; plaintiff appealed only negligence claim and court reversed, noting that California negligence law on deadly force was broader than Fourth Amendment and that officer’s pre-shooting conduct could render his behavior unreasonable; jury could find: that officer had reason to be aware that decedent was mentally ill, that officer failed to follow police protocol dealing with mentally ill persons before using force, that officer failed to deescalate th