fix: preserve binary response bodies in curl and HTTP bridge (#178)

* fix: preserve binary response bodies in curl and HTTP bridge

* fix: pass bodyBase64 through sync-backend so Python response.content is populated

- httpRequest() return type now includes bodyBase64 alongside body
- Python's _JbHttpResponse.content was always empty bytes due to
bodyBase64 being stripped
- add test covering binary response bodies (PNG bytes round-trip)