When a hospital system with thousands of employees is bleeding $10 million a month, tension is going to come to a head at some point. But news Friday that the Los Altos Hills-based Daughters of Charity Health System's six hospitals and foundation are set to be sold to for-profit Southern California conglomerate Prime Healthcare Services for $300 million in cash and $450 million in other financial pledges represents much more than a business transaction. The deal underscores simmering political controversy, financial turmoil and anxiety about how to deliver quality medical care at lower costs — realities that Silicon Valley, like much of the rest of the United States, is now being forced to confront amid a rapidly changing healthcare landscape.