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/main/java/org/raddatz/familienarchiv/service/OcrTrainingService.java

@@ -27,6 +27,7 @@ public class OcrTrainingService {
 
     private final OcrTrainingRunRepository trainingRunRepository;
     private final TrainingDataExportService trainingDataExportService;
+    private final SegmentationTrainingExportService segmentationTrainingExportService;
     private final OcrClient ocrClient;
     private final OcrHealthClient ocrHealthClient;
     private final TranscriptionBlockRepository blockRepository;
@@ -35,6 +36,7 @@ public class OcrTrainingService {
             int availableBlocks,
             int totalOcrBlocks,
             int availableDocuments,
+            int availableSegBlocks,
             boolean ocrServiceAvailable,
             OcrTrainingRun lastRun,
             List<OcrTrainingRun> runs
@@ -105,6 +107,7 @@ public class OcrTrainingService {
                 .count();
 
         int totalOcrBlocks = blockRepository.findAll().size();
+        int availableSegBlocks = segmentationTrainingExportService.querySegmentationBlocks().size();
 
         List<OcrTrainingRun> recentRuns = trainingRunRepository.findTop5ByOrderByCreatedAtDesc();
         OcrTrainingRun lastRun = recentRuns.isEmpty() ? null : recentRuns.get(0);
@@ -113,6 +116,7 @@ public class OcrTrainingService {
                 eligibleBlocks.size(),
                 totalOcrBlocks,
                 availableDocuments,
+                availableSegBlocks,
                 ocrHealthClient.isHealthy(),
                 lastRun,
                 recentRuns
@@ -139,6 +143,7 @@ public class OcrTrainingService {
                 "availableBlocks", info.availableBlocks(),
                 "totalOcrBlocks", info.totalOcrBlocks(),
                 "availableDocuments", info.availableDocuments(),
+                "availableSegBlocks", info.availableSegBlocks(),
                 "ocrServiceAvailable", info.ocrServiceAvailable(),
                 "lastRun", info.lastRun() != null ? info.lastRun() : Map.of(),
                 "runs", info.runs()