feat(ocr): show translated progress messages during OCR processing

Backend sends progress codes (PREPARING, LOADING, ANALYZING,
CREATING_BLOCKS:N, DONE:N, ERROR) via OcrJob.progressMessage.
Frontend translates them via Paraglide (de/en/es) and displays
below the spinner.

- V27 migration: adds progress_message column to ocr_jobs
- OcrAsyncRunner updates progress at each phase
- Poll interval reduced to 2s for snappier updates

Refs #226

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

frontend/messages/es.json

@@ -521,6 +521,12 @@
 	"ocr_error_retry": "Intentar de nuevo",
 	"ocr_batch_running": "OCR en curso · {processed} de {total} documentos completados",
 	"ocr_batch_done": "OCR completado · {processed} exitosos · {errors} fallidos",
+	"ocr_status_preparing": "Preparando documento…",
+	"ocr_status_loading": "Cargando modelo y documento…",
+	"ocr_status_analyzing": "Análisis OCR en curso — esto puede tardar unos minutos…",
+	"ocr_status_creating_blocks": "{count} bloques de texto detectados — creando transcripción…",
+	"ocr_status_done_blocks": "{count} bloques creados",
+	"ocr_status_error": "OCR fallido",
 	"transcription_block_review": "Marcar como revisado",
 	"transcription_block_unreview": "Desmarcar como revisado",
 	"transcription_reviewed_count": "{reviewed} de {total} revisados"