feat(ocr): add PREPROCESSING_PAGE progress translation and i18n strings

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

frontend/messages/de.json

@@ -526,6 +526,7 @@
 	"ocr_status_creating_blocks": "{count} Textblöcke erkannt — erstelle Transkription…",
 	"ocr_status_done_blocks": "{count} Blöcke erstellt",
 	"ocr_status_analyzing_page": "Seite {current} von {total} wird analysiert…",
+	"ocr_status_preprocessing_page": "Seite {current} von {total} wird aufbereitet…",
 	"ocr_status_done_skipped": "{count} Blöcke erstellt, {skipped} Seite(n) übersprungen",
 	"ocr_status_error": "OCR fehlgeschlagen",
 	"ocr_trigger_no_annotations": "Zeichnen Sie zuerst Bereiche auf dem Dokument ein.",

frontend/messages/en.json

@@ -526,6 +526,7 @@
 	"ocr_status_creating_blocks": "{count} text blocks detected — creating transcription…",
 	"ocr_status_done_blocks": "{count} blocks created",
 	"ocr_status_analyzing_page": "Analyzing page {current} of {total}…",
+	"ocr_status_preprocessing_page": "Preparing page {current} of {total}…",
 	"ocr_status_done_skipped": "{count} blocks created, {skipped} page(s) skipped",
 	"ocr_status_error": "OCR failed",
 	"ocr_trigger_no_annotations": "Draw regions on the document first.",

frontend/messages/es.json

@@ -526,6 +526,7 @@
 	"ocr_status_creating_blocks": "{count} bloques de texto detectados — creando transcripción…",
 	"ocr_status_done_blocks": "{count} bloques creados",
 	"ocr_status_analyzing_page": "Analizando página {current} de {total}…",
+	"ocr_status_preprocessing_page": "Preparando página {current} de {total}…",
 	"ocr_status_done_skipped": "{count} bloques creados, {skipped} página(s) omitida(s)",
 	"ocr_status_error": "OCR fallido",
 	"ocr_trigger_no_annotations": "Dibuje regiones en el documento primero.",