After five years of massive struggles, Jackson Health System finished in the black for the fiscal year that ended Sept. 30, the chief financial officer said Thursday. After losing $419 million the previous three years, Mark Knight said year-end financial adjustments mean Jackson, the safety net hospital for Miami-Dade County's poor and uninsured, will show a slight surplus for the year. Last year, the situation was so dire that a Boston for-profit hospital system offered to take over Jackson to protect the county government from having to pay Jackson's bills if the hospitals couldn't meet payroll.