add: register and login with DB query AND some struct type correction

internal/api/models/patient.go

@@ -4,6 +4,7 @@ package models
 type PatientDetails struct {
 	PatientID         string   `json:"patient_id"`
 	PatientName       string   `json:"patient_name"`
+	DateOfBirth       string   `json:"date_of_birth"` // YYYY-MM-DD format
 	StudyInstanceUIDs []string `json:"study_instance_uids,omitempty"`
 	AccessionNumbers  []string `json:"accession_numbers,omitempty"`
 }