Fix: Ensure BudgetProvider usage

The `useBudget` hook was being called outside of the `BudgetProvider` context in the `Index` component. This commit ensures that the `Index` component and its children are wrapped with the `BudgetProvider` in `App.tsx` to resolve the error.

src/contexts/budget/BudgetContext.tsx

@@ -20,4 +20,5 @@ export { useBudget } from './useBudget';
 export type { BudgetContextType } from './useBudget';
 
 // types.ts에서 타입들을 export
-export { BudgetPeriod, Transaction } from './types';
+export { BudgetPeriod } from './types';
+export type { Transaction } from './types';