WASHINGTON — A deadline burst of sign-ups after a tumultuous year for the Obama health law has revealed continued demand for the program’s subsidized individual health plans. But the Affordable Care Act’s troubles aren’t over. On the plus side for the overhaul, official numbers showed a sizable share of first-time customers, 36 percent, were among those rushing to finish HealthCare.gov applications in the run-up to Friday’s enrollment deadline. “People need health care, that is plain and simple,” said Kevin Watkins of Florence, Alabama.