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/routes/admin/system/page.svelte.spec.ts

@@ -78,6 +78,8 @@ describe('Admin system page — mass import card', () => {
 					startedAt: null
 				})
 			})
+			// training info fetch → empty
+			.mockResolvedValueOnce({ ok: true, json: async () => ({}) })
 			// trigger POST → returns RUNNING immediately
 			.mockResolvedValueOnce({
 				ok: true,