Add role-based visibility controls for UI elements

• Create new CSS visibility classes based on user roles and permissions
• Update ApplicationHelper to add data attributes to body based on user roles and permissions
• Replace legacy hide-unless-shiftcoordinator with more specific can-manage-assignments-only
• Support both positive (has-role-X-only) and negative (except-has-role-X) visibility rules
• Maintain backward compatibility with existing shiftcoordinator checks