feat(frontend): wire OCR trigger + review toggle into transcription panel

- OcrTrigger component rendered in the transcription empty state when
  the document has a file and user has write permission
- Review checkmark toggle on each TranscriptionBlock (turquoise when
  reviewed, muted outline when not). Calls PUT .../review to toggle.
- TranscriptionBlockData type: added source + reviewed fields
- +page.svelte: triggerOcr() and reviewToggle() functions wired up
- Paraglide translations (de/en/es) for review toggle + reviewed count

All 687 frontend tests pass.

Refs #226, #230

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

frontend/messages/de.json

@@ -520,5 +520,8 @@
 	"ocr_error_heading": "OCR fehlgeschlagen",
 	"ocr_error_retry": "Erneut versuchen",
 	"ocr_batch_running": "OCR läuft · {processed} von {total} Dokumente abgeschlossen",
-	"ocr_batch_done": "OCR abgeschlossen · {processed} erfolgreich · {errors} fehlgeschlagen"
+	"ocr_batch_done": "OCR abgeschlossen · {processed} erfolgreich · {errors} fehlgeschlagen",
+	"transcription_block_review": "Als geprüft markieren",
+	"transcription_block_unreview": "Markierung aufheben",
+	"transcription_reviewed_count": "{reviewed} von {total} geprüft"
 }