v0.3.7

Fixed

• explain_query appeared to return only the version envelope in 0.3.6:
  it was the one tool without structured content, and hosts that show
  structured content in preference to text saw nothing else. It now returns
  physical_plan and sections as structured JSON alongside the Markdown.

Added

• Error results end with the server name and version, so the build is
  identifiable exactly when a bug report needs it. (Errors cannot carry
  structured content: clients validate it against run_query's output
  schema even for errors.)