test(import): add IMPORT_DONE statusCode service test

Covers the success path — previously untested per Sara's review.
Creates a minimal empty XLSX via XSSFWorkbook so processRows returns 0.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/importing/MassImportServiceTest.java

@@ -20,7 +20,10 @@ import software.amazon.awssdk.core.sync.RequestBody;
 import software.amazon.awssdk.services.s3.S3Client;
 import software.amazon.awssdk.services.s3.model.PutObjectRequest;
 
+import org.apache.poi.xssf.usermodel.XSSFWorkbook;
+
 import java.io.File;
+import java.io.OutputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.time.LocalDate;
@@ -108,6 +111,22 @@ class MassImportServiceTest {
         assertThat(service.getStatus().statusCode()).isEqualTo("IMPORT_FAILED_NO_SPREADSHEET");
     }
 
+    @Test
+    void runImportAsync_setsStatusCode_IMPORT_DONE_whenSpreadsheetHasNoDataRows(@TempDir Path tempDir) throws Exception {
+        Path xlsx = tempDir.resolve("import.xlsx");
+        try (XSSFWorkbook wb = new XSSFWorkbook()) {
+            wb.createSheet("Sheet1");
+            try (OutputStream out = Files.newOutputStream(xlsx)) {
+                wb.write(out);
+            }
+        }
+        ReflectionTestUtils.setField(service, "importDir", tempDir.toString());
+
+        service.runImportAsync();
+
+        assertThat(service.getStatus().statusCode()).isEqualTo("IMPORT_DONE");
+    }
+
     @Test
     void runImportAsync_throwsConflict_whenAlreadyRunning() {
         MassImportService.ImportStatus running = new MassImportService.ImportStatus(