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>

Dockerfile

@@ -21,11 +21,13 @@ COPY --from=builder /usr/local/bin /usr/local/bin
 #   ghostscript     – required by ocrmypdf for PDF/PS operations
 #   poppler-utils   – provides pdfinfo/pdftoppm used by pdf2image
 #   unpaper         – optional deskewing pre-processor used by ocrmypdf
+#   wget            – used by ocr_language_manager to download tessdata files
 RUN apt-get update && apt-get install -y --no-install-recommends \
         tesseract-ocr \
         ghostscript \
         poppler-utils \
         unpaper \
+        wget \
     && apt-get clean && rm -rf /var/lib/apt/lists/*
 
 # Copy application code