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/en.json

@@ -521,6 +521,12 @@
 	"ocr_error_retry": "Try again",
 	"ocr_batch_running": "OCR running · {processed} of {total} documents complete",
 	"ocr_batch_done": "OCR complete · {processed} successful · {errors} failed",
+	"ocr_status_preparing": "Preparing document…",
+	"ocr_status_loading": "Loading model and document…",
+	"ocr_status_analyzing": "OCR analysis running — this may take a few minutes…",
+	"ocr_status_creating_blocks": "{count} text blocks detected — creating transcription…",
+	"ocr_status_done_blocks": "{count} blocks created",
+	"ocr_status_error": "OCR failed",
 	"transcription_block_review": "Mark as reviewed",
 	"transcription_block_unreview": "Unmark as reviewed",
 	"transcription_reviewed_count": "{reviewed} of {total} reviewed"