feat(import): add structured statusCode to ImportStatus — replaces raw German message

Adds a statusCode field (IMPORT_IDLE / IMPORT_RUNNING / IMPORT_DONE /
IMPORT_FAILED_NO_SPREADSHEET / IMPORT_FAILED_INTERNAL) to ImportStatus.
The frontend will map these codes to localized strings via Paraglide
instead of rendering the backend's German message verbatim.

NoSpreadsheetException distinguishes a missing spreadsheet from other
I/O failures so the frontend can show a specific error without raw text.

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

backend/src/main/java/org/raddatz/familienarchiv/importing/MassImportService.java

@@ -52,9 +52,9 @@ public class MassImportService {
 
     public enum State { IDLE, RUNNING, DONE, FAILED }
 
-    public record ImportStatus(State state, String message, int processed, LocalDateTime startedAt) {}
+    public record ImportStatus(State state, String statusCode, String message, int processed, LocalDateTime startedAt) {}
 
-    private volatile ImportStatus currentStatus = new ImportStatus(State.IDLE, "Kein Import gestartet.", 0, null);
+    private volatile ImportStatus currentStatus = new ImportStatus(State.IDLE, "IMPORT_IDLE", "Kein Import gestartet.", 0, null);
 
     public ImportStatus getStatus() {
         return currentStatus;
@@ -116,20 +116,29 @@ public class MassImportService {
         if (currentStatus.state() == State.RUNNING) {
             throw DomainException.conflict(ErrorCode.IMPORT_ALREADY_RUNNING, "A mass import is already in progress");
         }
-        currentStatus = new ImportStatus(State.RUNNING, "Import läuft...", 0, LocalDateTime.now());
+        currentStatus = new ImportStatus(State.RUNNING, "IMPORT_RUNNING", "Import läuft...", 0, LocalDateTime.now());
         try {
             File spreadsheet = findSpreadsheetFile();
             log.info("Starte Massenimport aus: {}", spreadsheet.getAbsolutePath());
             int processed = processRows(readSpreadsheet(spreadsheet));
-            currentStatus = new ImportStatus(State.DONE,
+            currentStatus = new ImportStatus(State.DONE, "IMPORT_DONE",
                     "Import abgeschlossen. " + processed + " Dokumente verarbeitet.",
                     processed, currentStatus.startedAt());
+        } catch (NoSpreadsheetException e) {
+            log.error("Massenimport fehlgeschlagen: keine Tabellendatei", e);
+            currentStatus = new ImportStatus(State.FAILED, "IMPORT_FAILED_NO_SPREADSHEET",
+                    "Fehler: " + e.getMessage(), 0, currentStatus.startedAt());
         } catch (Exception e) {
             log.error("Massenimport fehlgeschlagen", e);
-            currentStatus = new ImportStatus(State.FAILED, "Fehler: " + e.getMessage(), 0, currentStatus.startedAt());
+            currentStatus = new ImportStatus(State.FAILED, "IMPORT_FAILED_INTERNAL",
+                    "Fehler: " + e.getMessage(), 0, currentStatus.startedAt());
         }
     }
 
+    private static class NoSpreadsheetException extends RuntimeException {
+        NoSpreadsheetException(String message) { super(message); }
+    }
+
     private File findSpreadsheetFile() throws IOException {
         try (Stream<Path> files = Files.list(Paths.get(importDir))) {
             return files
@@ -138,7 +147,7 @@ public class MassImportService {
                         return name.endsWith(".ods") || name.endsWith(".xlsx") || name.endsWith(".xls");
                     })
                     .findFirst()
-                    .orElseThrow(() -> new RuntimeException(
+                    .orElseThrow(() -> new NoSpreadsheetException(
                             "Keine Tabellendatei (.ods/.xlsx/.xls) in " + importDir + " gefunden!"))
                     .toFile();
         }

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

@@ -70,14 +70,20 @@ class MassImportServiceTest {
         assertThat(service.getStatus().state()).isEqualTo(MassImportService.State.IDLE);
     }
 
+    @Test
+    void getStatus_hasStatusCode_IMPORT_IDLE_byDefault() {
+        assertThat(service.getStatus().statusCode()).isEqualTo("IMPORT_IDLE");
+    }
+
     // ─── runImportAsync ───────────────────────────────────────────────────────
 
     @Test
     void runImportAsync_setsFailedStatus_whenImportDirectoryDoesNotExist() {
-        // /import directory doesn't exist in test environment → findSpreadsheetFile throws
+        // /import directory doesn't exist in test environment → IOException → IMPORT_FAILED_INTERNAL
         service.runImportAsync();
 
         assertThat(service.getStatus().state()).isEqualTo(MassImportService.State.FAILED);
+        assertThat(service.getStatus().statusCode()).isEqualTo("IMPORT_FAILED_INTERNAL");
     }
 
     @Test
@@ -93,10 +99,19 @@ class MassImportServiceTest {
         assertThat(service.getStatus().message()).contains(tempDir.toString());
     }
 
+    @Test
+    void runImportAsync_setsStatusCode_IMPORT_FAILED_NO_SPREADSHEET_whenDirIsEmpty(@TempDir Path tempDir) {
+        ReflectionTestUtils.setField(service, "importDir", tempDir.toString());
+
+        service.runImportAsync();
+
+        assertThat(service.getStatus().statusCode()).isEqualTo("IMPORT_FAILED_NO_SPREADSHEET");
+    }
+
     @Test
     void runImportAsync_throwsConflict_whenAlreadyRunning() {
         MassImportService.ImportStatus running = new MassImportService.ImportStatus(
-                MassImportService.State.RUNNING, "Running...", 0, LocalDateTime.now());
+                MassImportService.State.RUNNING, "IMPORT_RUNNING", "Running...", 0, LocalDateTime.now());
         ReflectionTestUtils.setField(service, "currentStatus", running);
 
         assertThatThrownBy(() -> service.runImportAsync())

backend/src/test/java/org/raddatz/familienarchiv/user/AdminControllerTest.java

@@ -40,6 +40,22 @@ class AdminControllerTest {
     @MockitoBean ThumbnailBackfillService thumbnailBackfillService;
     @MockitoBean CustomUserDetailsService customUserDetailsService;
 
+    // ─── GET /api/admin/import-status ─────────────────────────────────────────
+
+    @Test
+    @WithMockUser(authorities = "ADMIN")
+    void importStatus_returns200_withStatusCode_whenAdmin() throws Exception {
+        MassImportService.ImportStatus status = new MassImportService.ImportStatus(
+                MassImportService.State.IDLE, "IMPORT_IDLE", "Kein Import gestartet.", 0, null);
+        when(massImportService.getStatus()).thenReturn(status);
+
+        mockMvc.perform(get("/api/admin/import-status"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.state").value("IDLE"))
+                .andExpect(jsonPath("$.statusCode").value("IMPORT_IDLE"))
+                .andExpect(jsonPath("$.processed").value(0));
+    }
+
     @Test
     void backfillVersions_returns401_whenUnauthenticated() throws Exception {
         mockMvc.perform(post("/api/admin/backfill-versions"))