fix: prevent duplicate consultations in backend, health calendar shows medication dots

backend/src/HealthManager.Application/Services/ConsultationService.cs

@@ -28,6 +28,12 @@ public class ConsultationService(AppDbContext db)
 
     public async Task<Consultation> StartAsync(Guid patientId, Guid doctorId, string subject)
     {
+        // Reuse existing active consultation between this patient and doctor
+        var existing = await db.Consultations
+            .FirstOrDefaultAsync(c => c.PatientId == patientId && c.DoctorId == doctorId && c.Status == "active");
+        if (existing != null)
+            return existing;
+
         var consultation = new Consultation
         {
             PatientId = patientId,