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>