Fix: Handle undefined budget data

The `useBudgetTabContent` hook was throwing an error when `data` prop was undefined. This commit adds a check to ensure that `data` is defined before accessing its properties.

src/components/BudgetTabContent.tsx

@@ -13,7 +13,7 @@ interface BudgetData {
   remainingAmount: number;
 }
 
-interface BudgetTabContentProps {
+export interface BudgetTabContentProps {
   data: BudgetData;
   formatCurrency: (amount: number) => string;
   calculatePercentage: (spent: number, target: number) => number;
@@ -26,6 +26,12 @@ const BudgetTabContent: React.FC<BudgetTabContentProps> = ({
   calculatePercentage,
   onSaveBudget
 }) => {
+  // 데이터 유효성 체크 - 데이터가 없으면 기본값 사용
+  if (!data) {
+    console.warn('BudgetTabContent: data prop이 제공되지 않았습니다. 기본값을 사용합니다.');
+    data = { targetAmount: 0, spentAmount: 0, remainingAmount: 0 };
+  }
+
   const {
     categoryBudgets,
     showBudgetInput,