[FEATURE REQUEST] Be able to return binary data (images) from endpoints

### Feature Summary
- Endpoints should be able to return a file instead of JSON

### Justification/Rationale
- For a potential use case of generative AI, or also e.g. returning stored frames, it would be good to be able to return images.

### Proposed Implementation (if any)
- The endpoint definition could have a flag that lets you say the output should be interpreted as a file.

No file or test is named in the issue. Begin at the endpoint definition and trace how responses are currently serialized; done means endpoints can return binary image data while existing JSON responses continue to work.

Written by the indexing model from the issue text.