Adds optional save_to_s3=True to convert_document. After conversion,
the text output is uploaded to chat-artifacts S3 and s3_url is returned
alongside the result. Also fixes boto3 1.35+ checksum regression
(request_checksum_calculation=when_required) and adds boto3 dep.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
root
fkrebs