refactor: Centralize database session management in a shared dependency module

routes/simulations.py

@@ -1,27 +1,19 @@
-from typing import List, Optional, cast
+from typing import Dict, List, Optional
 
 from fastapi import APIRouter, Depends, HTTPException, status
 from pydantic import BaseModel, PositiveInt
 from sqlalchemy.orm import Session
 
-from config.database import SessionLocal
 from models.parameters import Parameter
 from models.scenario import Scenario
 from models.simulation_result import SimulationResult
+from routes.dependencies import get_db
 from services.reporting import generate_report
 from services.simulation import run_simulation
 
 router = APIRouter(prefix="/api/simulations", tags=["Simulations"])
 
 
-def get_db():
-    db = SessionLocal()
-    try:
-        yield db
-    finally:
-        db.close()
-
-
 class SimulationParameterInput(BaseModel):
     name: str
     value: float
@@ -48,7 +40,7 @@ class SimulationRunResponse(BaseModel):
     scenario_id: int
     iterations: int
     results: List[SimulationResultItem]
-    summary: dict
+    summary: Dict[str, float | int]
 
 
 def _load_parameters(db: Session, scenario_id: int) -> List[SimulationParameterInput]: