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>

frontend/src/lib/generated/api.ts

@@ -1429,6 +1429,8 @@ export interface components {
             totalOcrBlocks?: number;
             /** Format: int32 */
             availableDocuments?: number;
+            /** Format: int32 */
+            availableSegBlocks?: number;
             ocrServiceAvailable?: boolean;
             lastRun?: components["schemas"]["OcrTrainingRun"];
             runs?: components["schemas"]["OcrTrainingRun"][];