feat: add Excel data validation functionality

- Implemented a new API endpoint for validating Excel data before upload, ensuring that required fields are not null and that unique constraints are respected.
- Added frontend integration to handle validation results, displaying errors for missing required fields and duplicates within the Excel file and against existing database records.
- Enhanced user experience by providing immediate feedback on data validity during the upload process.

Made-with: Cursor

frontend/lib/api/tableManagement.ts

@@ -372,3 +372,30 @@ export const getTableColumns = (tableName: string) => tableManagementApi.getColu
 export const updateColumnType = (tableName: string, columnName: string, settings: ColumnSettings) =>
   tableManagementApi.updateColumnSettings(tableName, columnName, settings);
 export const checkTableExists = (tableName: string) => tableManagementApi.checkTableExists(tableName);
+
+// 엑셀 업로드 전 데이터 검증 API
+export interface ExcelValidationResult {
+  isValid: boolean;
+  notNullErrors: { row: number; column: string; label: string }[];
+  uniqueInExcelErrors: { rows: number[]; column: string; label: string; value: string }[];
+  uniqueInDbErrors: { row: number; column: string; label: string; value: string }[];
+  summary: { notNull: number; uniqueInExcel: number; uniqueInDb: number };
+}
+
+export async function validateExcelData(
+  tableName: string,
+  data: Record<string, any>[]
+): Promise<ApiResponse<ExcelValidationResult>> {
+  try {
+    const response = await apiClient.post<ApiResponse<ExcelValidationResult>>(
+      "/table-management/validate-excel",
+      { tableName, data }
+    );
+    return response.data;
+  } catch (error: any) {
+    return {
+      success: false,
+      message: error.response?.data?.message || "데이터 검증 실패",
+    };
+  }
+}