Expose lost/won reason fields on public opportunity endpoint

Description:

The internal API includes lostReason, lostReasonNote, and related fields on opportunity objects, but these are not returned by GET /public-api/opportunity or GET /public-api/opportunity/{id}, and they're absent from the Swagger model.

Requested by W.T. Solutions (Peter van der Waal) who is building an integration and needs to read closed opportunity reasons via the public API.

Per dev confirmation there are no technical blockers — the fields just weren't included due to lack of prior demand.

Acceptance criteria:

lostReason and lostReasonNote (and any other reason-related fields present in the internal model) are returned in the public opportunity response and documented in Swagger.