JDK HttpClient defaults to HTTP/2 with upgrade negotiation. Uvicorn
rejects the upgrade ('Unsupported upgrade request'), causing the
request body to be lost and a 422 'Field required' from FastAPI.
Force HTTP/1.1 since the OCR service is internal and doesn't need h2.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>