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/src/lib/errors.ts

@@ -26,6 +26,7 @@ export type ErrorCode =
 	| 'OCR_JOB_NOT_FOUND'
 	| 'OCR_DOCUMENT_NOT_UPLOADED'
 	| 'OCR_PROCESSING_FAILED'
+	| 'TRAINING_ALREADY_RUNNING'
 	| 'UNAUTHORIZED'
 	| 'FORBIDDEN'
 	| 'VALIDATION_ERROR'
@@ -97,6 +98,8 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 			return m.error_ocr_document_not_uploaded();
 		case 'OCR_PROCESSING_FAILED':
 			return m.error_ocr_processing_failed();
+		case 'TRAINING_ALREADY_RUNNING':
+			return m.error_training_already_running();
 		case 'UNAUTHORIZED':
 			return m.error_unauthorized();
 		case 'FORBIDDEN':