Overworked UPMC nurses face staffing shortages and other issues in their efforts to treat mental health challenges in Allegheny County. Providers and mental health experts rallied on Sept. 24 at the UPMC Western Psychiatric Hospital to underline what they say is a crisis of management colliding with what experts call a national crisis of poor mental health. UPMC nurses say the system’s — and region’s — biggest mental healthcare facility is at an inflection point…