fix: prevent duplicate consultations with db unique constraint, frontend init once guard, chat history preserved

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

@@ -41,7 +41,19 @@ public class ConsultationService(AppDbContext db)
             Subject = subject,
         };
         db.Consultations.Add(consultation);
-        await db.SaveChangesAsync();
+        try
+        {
+            await db.SaveChangesAsync();
+        }
+        catch (DbUpdateException)
+        {
+            // Race condition: another request created one between our check and save
+            // The unique index on (PatientId, DoctorId) where Status='active' caught it
+            db.ChangeTracker.Clear();
+            var retry = await db.Consultations
+                .FirstOrDefaultAsync(c => c.PatientId == patientId && c.DoctorId == doctorId && c.Status == "active");
+            return retry!;
+        }
         return consultation;
     }