### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

The SAP orchestration service supports file inputs on user messages (added in `b822da9` on the SAP side — "File inputs have a type of `file` and include a `file_data` field ... Local files must be provided as `data:MEDIATYPE;base64,DATA`"). The service accepts them today for Anthropic and Gemini models.

LiteLLM cannot send them. `SAPUserMessage.content` only models `text` and `image_url` parts, so a file part fails pydantic validation before any request leaves the client:

``` litellm.APIConnectionError: 7 validation errors for SAPUserMessage content.str Input should be a valid string [type=string_type, input_type=list] content.TextContent Input should be a valid dictionary or instance of TextContent [type=model_type, input_type=list] content.ImageContent Input should be a valid dictionary or instance of ImageContent [type=model_type, input_type=list] content.list[union[TextContent,ImageContent]].1.TextContent.type Input should be 'text' [type=literal_error, input_value='file', input_type=str] content.list[union[TextContent,ImageConten…