feat: integrate Tesseract.js with improved language availability and font handling

- Refactored OCR page recognition to utilize a configured Tesseract worker.
- Added functions to manage font URLs and asset filenames based on language.
- Implemented language availability checks and error handling for unsupported languages.
- Enhanced PDF workflow to display available OCR languages and handle user selections.
- Introduced utility functions for resolving Tesseract asset configurations.
- Added tests for OCR functionality, font loading, and Tesseract runtime behavior.
- Updated global types to include environment variables for Tesseract and font configurations.

.env.example

@@ -12,6 +12,15 @@ VITE_WASM_PYMUPDF_URL=https://cdn.jsdelivr.net/npm/@bentopdf/pymupdf-wasm@0.11.1
 VITE_WASM_GS_URL=https://cdn.jsdelivr.net/npm/@bentopdf/gs-wasm/assets/
 VITE_WASM_CPDF_URL=https://cdn.jsdelivr.net/npm/coherentpdf/dist/
 
+# OCR assets (optional)
+# Set all three together for self-hosted or air-gapped OCR.
+# Leave empty to use Tesseract.js runtime defaults.
+VITE_TESSERACT_WORKER_URL=
+VITE_TESSERACT_CORE_URL=
+VITE_TESSERACT_LANG_URL=
+VITE_TESSERACT_AVAILABLE_LANGUAGES=
+VITE_OCR_FONT_BASE_URL=
+
 # Default UI language (build-time)
 # Supported: en, ar, be, fr, de, es, zh, zh-TW, vi, tr, id, it, pt, nl, da
 VITE_DEFAULT_LANGUAGE=