refactor: Replace local Base declaration with import from config.database

models/performance_metric.py

@@ -3,9 +3,8 @@ from __future__ import annotations
 from datetime import datetime
 
 from sqlalchemy import Column, DateTime, Float, Integer, String
-from sqlalchemy.ext.declarative import declarative_base
 
-Base = declarative_base()
+from config.database import Base
 
 
 class PerformanceMetric(Base):