feat(admin): add OCR training card to admin/system page

- TrainingHistory.svelte: responsive table with status badges
  (green/red/animated pulse), keyed iteration, empty-state row
- OcrTrainingCard.svelte: shows available blocks/docs, disabled states
  (< 5 blocks, service down), in-flight "…" state, 5s success message,
  embeds TrainingHistory
- Wired into admin/system/+page.svelte via fetchTrainingInfo() in $effect
- Regenerated api.ts with OcrTrainingRun + TrainingInfoResponse types
- TRAINING_ALREADY_RUNNING error code in errors.ts + de/en/es translations
- 7 OcrTrainingCard Vitest tests

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

frontend/messages/es.json

@@ -505,6 +505,7 @@
 	"error_ocr_job_not_found": "No se encontró el trabajo OCR.",
 	"error_ocr_document_not_uploaded": "El documento no tiene archivo — OCR no es posible.",
 	"error_ocr_processing_failed": "El procesamiento OCR ha fallado.",
+	"error_training_already_running": "Ya hay un proceso de entrenamiento en curso.",
 	"ocr_script_type_typewriter": "Máquina de escribir",
 	"ocr_script_type_handwriting_latin": "Escritura manuscrita (latina)",
 	"ocr_script_type_handwriting_kurrent": "Escritura manuscrita (Kurrent/Sütterlin)",