A 6-week-old female infant presents to an outpatient pediatric clinic for a routine follow-up. She was born at 33 weeks gestation to a 28-year-old primigravida who reported a mild, self-limiting febrile illness during her second trimester, initially dismissed as a common cold. The infant's parents express concerns about poor feeding, persistent irritability, and an exaggerated startle response to sudden noises. On physical examination, a diffuse "blueberry muffin" rash, consisting of non-blanchable, non-palpable red-purple macules, is observed over her scalp and trunk. Ophthalmic evaluation reveals bilateral chorioretinal scars with areas of active inflammation. Neurological assessment notes increased generalized tone and a hyperactive Moro reflex. Her head circumference is above the 90th percentile for age, and the anterior fontanelle is full and bulging. A recent head imaging study (similar to Figure A, demonstrating significant findings) revealed widespread ventriculomegaly and scattered intraparenchymal calcifications. Her current weight is noted to be below the 5th percentile for corrected age. Laboratory results are pending. Based on these findings, what is the most likely diagnosis and the appropriate initial medical management?