Add validation for uploaded file data format

src/App.jsx

@@ -29,6 +29,21 @@ function App() {
         const sheetName = workbook.SheetNames[0];
         const worksheet = workbook.Sheets[sheetName];
         const jsonData = utils.sheet_to_json(worksheet, {raw:true});
+
+        if (jsonData.length === 0) {
+          alert("파일에 데이터가 없습니다.");
+          return;
+        }
+
+        const columns = Object.keys(jsonData[0]);
+        const requiredColumns = ['address', 'amount'];
+
+        if (columns.length !== 2 ||
+            !requiredColumns.every(col => columns.includes(col))) {
+          alert("양식이 맞지 않습니다.");
+          return;
+        }
+
         let total = totalAmount;
 
         const filteredData = jsonData.filter(row => {