fix: move Optional import to top of feature_engineer.py

app/services/feature_engineer.py

@@ -1,7 +1,7 @@
 """Feature engineering for TFT stock price prediction."""
 import numpy as np
 import pandas as pd
-from typing import Tuple
+from typing import Optional, Tuple
 
 
 SEQUENCE_LEN = 60   # lookback window (TFT benefits from longer context)
@@ -128,9 +128,6 @@ def build_features(
     return features.astype(np.float32)
 
 
-# Optional type hint (Python 3.10+)
-from typing import Optional
-
 
 def make_sequences(
     features: np.ndarray,