fix(ocr): use camelCase field names in Pydantic models

Pydantic v2 Field(alias=...) doesn't work with FastAPI as expected.
The Java client sends camelCase (pdfUrl, scriptType, pageNumber).
Use camelCase field names directly instead of aliases.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ocr-service/main.py

@@ -56,9 +56,9 @@ async def run_ocr(request: OcrRequest):
     if not _models_ready:
         raise HTTPException(status_code=503, detail="Models not loaded yet")
 
-    images = await _download_and_convert_pdf(request.pdf_url)
+    images = await _download_and_convert_pdf(request.pdfUrl)
 
-    script_type = request.script_type.upper()
+    script_type = request.scriptType.upper()
 
     if script_type == "HANDWRITING_KURRENT":
         if not kraken_engine.is_available():