refactor: Centralize database session management in a shared dependency module

routes/costs.py

@@ -1,23 +1,17 @@
-from fastapi import APIRouter, Depends
-from sqlalchemy.orm import Session
 from typing import List, Optional
+
+from fastapi import APIRouter, Depends
 from pydantic import BaseModel, ConfigDict
-from config.database import SessionLocal
+from sqlalchemy.orm import Session
+
 from models.capex import Capex
 from models.opex import Opex
+from routes.dependencies import get_db
 
 router = APIRouter(prefix="/api/costs", tags=["Costs"])
-
-
-def get_db():
-    db = SessionLocal()
-    try:
-        yield db
-    finally:
-        db.close()
-
-
 # Pydantic schemas for Capex
+
+
 class CapexCreate(BaseModel):
     scenario_id: int
     amount: float