fix admin.py

app/backend/routes/admin.py

@@ -213,17 +213,14 @@ def get_user_statistics(
 
     # Count users by creation date
     user_counts = session.exec(
-        select(
-            func.strftime("%Y-%m-%d", User.created_at).label("day"),
-            func.count().label("count"),
-        )
+        select(func.date(User.created_at).label("day"), func.count().label("count"))
         .where(User.created_at >= start_date)
-        .group_by(func.strftime("%Y-%m-%d", User.created_at))
+        .group_by(func.date(User.created_at))
     ).all()
 
     # Update counts
     for day_data in user_counts:
-        day_str = day_data[0]  # Now it's already in the correct string format
+        day_str = day_data[0].strftime("%Y-%m-%d")
         users_by_day[day_str] = day_data[1]
 
     # Convert to list of dictionaries