Route HTTPException (app- and framework-raised), RequestValidationError
and uncaught exceptions through build_error_response so every error body
is {detail, error_code, report?, trace?}. Fixes the bare-string body that
string HTTPException details produced, and registers the handler on the
Starlette base HTTPException so framework 404/405/415 also carry the full
envelope.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
