feat(training): add Paraglide i18n to training UI components and wire SegmentationTrainingCard

- Convert TrainingHistory, OcrTrainingCard, SegmentationTrainingCard, and
  TranscriptionBlock "Nur Segmentierung" badge to use Paraglide message keys
- Add availableSegBlocks to TrainingInfoResponse to expose segmentation
  block count in the training info endpoint
- Wire SegmentationTrainingCard into admin/system page below OCR training card
- Update api.ts with availableSegBlocks field

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

backend/src/test/java/org/raddatz/familienarchiv/controller/OcrControllerTest.java

@@ -44,6 +44,7 @@ class OcrControllerTest {
     @MockitoBean UserService userService;
     @MockitoBean CustomUserDetailsService customUserDetailsService;
     @MockitoBean TrainingDataExportService trainingDataExportService;
+    @MockitoBean SegmentationTrainingExportService segmentationTrainingExportService;
     @MockitoBean OcrTrainingService ocrTrainingService;
 
     @Test
@@ -217,7 +218,7 @@ class OcrControllerTest {
     @WithMockUser(authorities = "ADMIN")
     void getTrainingInfo_returns200_withInfo() throws Exception {
         OcrTrainingService.TrainingInfoResponse info =
-                new OcrTrainingService.TrainingInfoResponse(5, 20, 2, true, null, List.of());
+                new OcrTrainingService.TrainingInfoResponse(5, 20, 2, 3, true, null, List.of());
         when(ocrTrainingService.getTrainingInfo()).thenReturn(info);
 
         mockMvc.perform(get("/api/ocr/training-info"))

backend/src/test/java/org/raddatz/familienarchiv/service/OcrTrainingServiceTest.java

@@ -25,6 +25,7 @@ class OcrTrainingServiceTest {
 
     OcrTrainingRunRepository runRepository;
     TrainingDataExportService exportService;
+    SegmentationTrainingExportService segExportService;
     OcrClient ocrClient;
     OcrHealthClient healthClient;
     TranscriptionBlockRepository blockRepository;
@@ -34,14 +35,16 @@ class OcrTrainingServiceTest {
     void setUp() {
         runRepository = mock(OcrTrainingRunRepository.class);
         exportService = mock(TrainingDataExportService.class);
+        segExportService = mock(SegmentationTrainingExportService.class);
         ocrClient = mock(OcrClient.class);
         healthClient = mock(OcrHealthClient.class);
         blockRepository = mock(TranscriptionBlockRepository.class);
 
-        service = new OcrTrainingService(runRepository, exportService, ocrClient, healthClient, blockRepository);
+        service = new OcrTrainingService(runRepository, exportService, segExportService, ocrClient, healthClient, blockRepository);
 
         when(blockRepository.findAll()).thenReturn(List.of());
         when(runRepository.findTop5ByOrderByCreatedAtDesc()).thenReturn(List.of());
+        when(segExportService.querySegmentationBlocks()).thenReturn(List.of());
     }
 
     // ─── Concurrent guard ─────────────────────────────────────────────────────