Fix customer list endpoint

app/auth.py

@@ -151,8 +151,15 @@ async def list_customers(
     current_admin: str = Depends(get_current_admin)
 ):
     """List all customers"""
-    customers = db.query(Customer).all()
-    return customers
+    try:
+        customers = db.query(Customer).all()
+        return customers
+    except Exception as e:
+        print(f"Error listing customers: {str(e)}")
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=f"Error listing customers: {str(e)}"
+        )
 
 @router.get("/customers/{customer_id}", response_model=dict)
 async def get_customer(