feat(ocr): auto-install Tesseract/EasyOCR languages from settings

- Add app/utils/ocr_language_manager.py: detects tessdata dir, downloads
  missing .traineddata files via wget/curl from tessdata_fast GitHub repo,
  pre-downloads EasyOCR models, exposes async background-thread helper
- TesseractOCRProvider.process() calls ensure_tesseract_languages() before
  running pytesseract; raises clear error if languages remain unavailable
- EasyOCRProvider.process() logs informational message when models download
- app/main.py: calls ensure_ocr_languages_async() at startup
- app/utils/settings_sync.py: triggers language re-check after every
  settings reload so UI changes take effect without container restart
- app/api/settings.py: adds POST /api/settings/install-ocr-languages
  endpoint for on-demand language installation from the admin UI
- Dockerfile: adds wget for runtime tessdata downloads
- docs/ConfigurationGuide.md: documents automatic language download
- tests/test_ocr_language_manager.py: 29 unit tests

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/main.py

@@ -69,6 +69,11 @@ async def lifespan(app: FastAPI):
     finally:
         db.close()
 
+    # Ensure OCR language data is available (background download, non-blocking)
+    from app.utils.ocr_language_manager import ensure_ocr_languages_async
+
+    ensure_ocr_languages_async()
+
     # Force settings dump to log for troubleshooting
     from app.utils.config_validator import dump_all_settings