- Fix md5srv.py to handle requests using Transfer-Encoding: chunked
  instead of Content-Length. Notehub sends binary web.post payloads
  chunked, causing post_data to read 0 bytes and write_file to
  return 400 "Request body is empty."
- Fix write_file to fall back to len(self.post_data) when the
  Content-Length header is absent, rather than calling int(None)
  and crashing with a 500.
- Add error logging to md5srv.py: on any failed request, log the
  Content-Length, Transfer-Encoding, and Content-Type headers along
  with the error code and message to aid future debugging.
- Capture Notecard USB trace output (req, comm, sync, mem) to
  trace.log during the test run and upload it as a CI artifact.
- Upload md5srv.log as a CI artifact so server-side failures are
  visible without needing to reproduce locally.

Commit message written by Claude.